diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1a1ae531b..b210009b0 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -57,6 +57,7 @@
 * **Breaking changes**
   * Changed `SpineShaderWithOutlineGUI` outline related methods from `private` to `protected virtual` to allow for custom shader GUI subclasses to switch to different outline shaders.
   * Changed `BoneFollower` and `BoneFollowerGraphic` methods `LateUpdate` and `Initialize` to `virtual` to allow easier overriding for e.g. positional offset in custom subclasses.
+  * `MeshGenerator` received a new optimization option to avoid rendering fully transparent attachments at slot alpha 0 by default. Comment out `#define SLOT_ALPHA_DISABLES_ATTACHMENT` in `MeshGenerator.cs` to revert to previous behaviour. You may only need this option disabled when utilizing a custom shader which uses vertex color alpha for purposes other than transparency.
   
 * **Changes of default values**
 
diff --git a/spine-unity/Assets/Spine/Runtime/spine-unity/Components/SkeletonAnimation.cs b/spine-unity/Assets/Spine/Runtime/spine-unity/Components/SkeletonAnimation.cs
index ed1c6a4dd..0033ef067 100644
--- a/spine-unity/Assets/Spine/Runtime/spine-unity/Components/SkeletonAnimation.cs
+++ b/spine-unity/Assets/Spine/Runtime/spine-unity/Components/SkeletonAnimation.cs
@@ -83,15 +83,11 @@ namespace Spine.Unity {
 		/// </summary>
 		public event UpdateBonesDelegate UpdateLocal { add { _UpdateLocal += value; } remove { _UpdateLocal -= value; } }
 
-		/// <summary><para>
+		/// <summary>
 		/// Occurs after the Skeleton's bone world space values are resolved (including all constraints).
 		/// Using this callback will cause the world space values to be solved an extra time.
 		/// Use this callback if want to use bone world space values, and also set bone local values.
-		/// </para><para>
-		/// When used in combination with PhysicsConstraints at your skeleton, you might want to consider adjusting
-		/// <see cref="MainPhysicsUpdate"/> and <see cref="AdditionalPhysicsUpdate"/> to save updates by setting one to
-		/// <see cref="Skeleton.Physics.Pose"/>.
-		/// </para></summary>
+		/// </summary>
 		public event UpdateBonesDelegate UpdateWorld { add { _UpdateWorld += value; } remove { _UpdateWorld -= value; } }
 
 		/// <summary>
@@ -109,15 +105,6 @@ namespace Spine.Unity {
 		/// Instance SkeletonAnimation.timeScale will still be applied.</summary>
 		[SerializeField] protected bool unscaledTime;
 		public bool UnscaledTime { get { return unscaledTime; } set { unscaledTime = value; } }
-
-		protected Skeleton.Physics mainPhysicsUpdate = Skeleton.Physics.Update;
-		protected Skeleton.Physics additionalPhysicsUpdate = Skeleton.Physics.Update;
-		/// <summary>Physics update mode used in the main call to skeleton.UpdateWorldTransform().</summary>
-		public Skeleton.Physics MainPhysicsUpdate { get { return mainPhysicsUpdate; } set { mainPhysicsUpdate = value; } }
-		/// <summary>Physics update mode used at optional additional calls to skeleton.UpdateWorldTransform(),
-		/// such as after the <see cref="UpdateWorld"/> callback if a method is subscribed at the UpdateWorld delegate.
-		/// </summary>
-		public Skeleton.Physics AdditionalPhysicsUpdate { get { return additionalPhysicsUpdate; } set { additionalPhysicsUpdate = value; } }
 		#endregion
 
 		#region Serialized state and Beginner API
@@ -278,11 +265,12 @@ namespace Spine.Unity {
 			if (_UpdateLocal != null)
 				_UpdateLocal(this);
 
-			UpdateWorldTransform(mainPhysicsUpdate);
-
-			if (_UpdateWorld != null) {
+			if (_UpdateWorld == null) {
+				UpdateWorldTransform(Skeleton.Physics.Update);
+			} else {
+				UpdateWorldTransform(Skeleton.Physics.Pose);
 				_UpdateWorld(this);
-				UpdateWorldTransform(additionalPhysicsUpdate);
+				UpdateWorldTransform(Skeleton.Physics.Update);
 			}
 
 			if (_UpdateComplete != null) {
diff --git a/spine-unity/Assets/Spine/Runtime/spine-unity/Components/SkeletonGraphic.cs b/spine-unity/Assets/Spine/Runtime/spine-unity/Components/SkeletonGraphic.cs
index 828e13ed5..6dffe771e 100644
--- a/spine-unity/Assets/Spine/Runtime/spine-unity/Components/SkeletonGraphic.cs
+++ b/spine-unity/Assets/Spine/Runtime/spine-unity/Components/SkeletonGraphic.cs
@@ -403,11 +403,12 @@ namespace Spine.Unity {
 			if (UpdateLocal != null)
 				UpdateLocal(this);
 
-			UpdateWorldTransform(mainPhysicsUpdate);
-
-			if (UpdateWorld != null) {
+			if (UpdateWorld == null) {
+				UpdateWorldTransform(Skeleton.Physics.Update);
+			} else {
+				UpdateWorldTransform(Skeleton.Physics.Pose);
 				UpdateWorld(this);
-				UpdateWorldTransform(additionalPhysicsUpdate);
+				UpdateWorldTransform(Skeleton.Physics.Update);
 			}
 
 			if (UpdateComplete != null)
@@ -644,15 +645,6 @@ namespace Spine.Unity {
 		[SerializeField] protected bool unscaledTime;
 		public bool UnscaledTime { get { return unscaledTime; } set { unscaledTime = value; } }
 
-		protected Skeleton.Physics mainPhysicsUpdate = Skeleton.Physics.Update;
-		protected Skeleton.Physics additionalPhysicsUpdate = Skeleton.Physics.Update;
-		/// <summary>Physics update mode used in the main call to skeleton.UpdateWorldTransform().</summary>
-		public Skeleton.Physics MainPhysicsUpdate { get { return mainPhysicsUpdate; } set { mainPhysicsUpdate = value; } }
-		/// <summary>Physics update mode used at optional additional calls to skeleton.UpdateWorldTransform(),
-		/// such as after the <see cref="UpdateWorld"/> callback if a method is subscribed at the UpdateWorld delegate.
-		/// </summary>
-		public Skeleton.Physics AdditionalPhysicsUpdate { get { return additionalPhysicsUpdate; } set { additionalPhysicsUpdate = value; } }
-
 		/// <summary> Occurs after the vertex data populated every frame, before the vertices are pushed into the mesh.</summary>
 		public event Spine.Unity.MeshGeneratorDelegate OnPostProcessVertices;
 
diff --git a/spine-unity/Assets/Spine/Runtime/spine-unity/Components/SkeletonMecanim.cs b/spine-unity/Assets/Spine/Runtime/spine-unity/Components/SkeletonMecanim.cs
index 5a2d35f88..f070690a5 100644
--- a/spine-unity/Assets/Spine/Runtime/spine-unity/Components/SkeletonMecanim.cs
+++ b/spine-unity/Assets/Spine/Runtime/spine-unity/Components/SkeletonMecanim.cs
@@ -63,15 +63,11 @@ namespace Spine.Unity {
 		/// Use this callback when you want to set bone local values.</summary>
 		public event UpdateBonesDelegate UpdateLocal { add { _UpdateLocal += value; } remove { _UpdateLocal -= value; } }
 
-		/// <summary><para>
+		/// <summary>
 		/// Occurs after the Skeleton's bone world space values are resolved (including all constraints).
 		/// Using this callback will cause the world space values to be solved an extra time.
 		/// Use this callback if want to use bone world space values, and also set bone local values.
-		/// </para><para>
-		/// When used in combination with PhysicsConstraints at your skeleton, you might want to consider adjusting
-		/// <see cref="MainPhysicsUpdate"/> and <see cref="AdditionalPhysicsUpdate"/> to save updates by setting one to
-		/// <see cref="Skeleton.Physics.Pose"/>.
-		/// </para></summary>
+		/// </summary>
 		public event UpdateBonesDelegate UpdateWorld { add { _UpdateWorld += value; } remove { _UpdateWorld -= value; } }
 
 		/// <summary>
@@ -82,15 +78,6 @@ namespace Spine.Unity {
 
 		[SerializeField] protected UpdateTiming updateTiming = UpdateTiming.InUpdate;
 		public UpdateTiming UpdateTiming { get { return updateTiming; } set { updateTiming = value; } }
-
-		protected Skeleton.Physics mainPhysicsUpdate = Skeleton.Physics.Update;
-		protected Skeleton.Physics additionalPhysicsUpdate = Skeleton.Physics.Update;
-		/// <summary>Physics update mode used in the main call to skeleton.UpdateWorldTransform().</summary>
-		public Skeleton.Physics MainPhysicsUpdate { get { return mainPhysicsUpdate; } set { mainPhysicsUpdate = value; } }
-		/// <summary>Physics update mode used at optional additional calls to skeleton.UpdateWorldTransform(),
-		/// such as after the <see cref="UpdateWorld"/> callback if a method is subscribed at the UpdateWorld delegate.
-		/// </summary>
-		public Skeleton.Physics AdditionalPhysicsUpdate { get { return additionalPhysicsUpdate; } set { additionalPhysicsUpdate = value; } }
 		#endregion
 
 		public override void Initialize (bool overwrite, bool quiet = false) {
@@ -170,11 +157,12 @@ namespace Spine.Unity {
 			if (_UpdateLocal != null)
 				_UpdateLocal(this);
 
-			UpdateWorldTransform(mainPhysicsUpdate);
-
-			if (_UpdateWorld != null) {
+			if (_UpdateWorld == null) {
+				UpdateWorldTransform(Skeleton.Physics.Update);
+			} else {
+				UpdateWorldTransform(Skeleton.Physics.Pose);
 				_UpdateWorld(this);
-				UpdateWorldTransform(additionalPhysicsUpdate);
+				UpdateWorldTransform(Skeleton.Physics.Update);
 			}
 
 			if (_UpdateComplete != null)
diff --git a/spine-unity/Assets/Spine/Runtime/spine-unity/ISkeletonAnimation.cs b/spine-unity/Assets/Spine/Runtime/spine-unity/ISkeletonAnimation.cs
index 67871d778..06dea7f70 100644
--- a/spine-unity/Assets/Spine/Runtime/spine-unity/ISkeletonAnimation.cs
+++ b/spine-unity/Assets/Spine/Runtime/spine-unity/ISkeletonAnimation.cs
@@ -63,8 +63,6 @@ namespace Spine.Unity {
 		event UpdateBonesDelegate UpdateComplete;
 		Skeleton Skeleton { get; }
 		UpdateTiming UpdateTiming { get; set; }
-		Skeleton.Physics MainPhysicsUpdate { get; set; }
-		Skeleton.Physics AdditionalPhysicsUpdate { get; set; }
 	}
 
 	/// <summary>Holds a reference to a SkeletonDataAsset.</summary>
diff --git a/spine-unity/Assets/Spine/package.json b/spine-unity/Assets/Spine/package.json
index 614478e58..b91afae20 100644
--- a/spine-unity/Assets/Spine/package.json
+++ b/spine-unity/Assets/Spine/package.json
@@ -2,7 +2,7 @@
 	"name": "com.esotericsoftware.spine.spine-unity",
 	"displayName": "spine-unity Runtime",
 	"description": "This plugin provides the spine-unity runtime core.",
-	"version": "4.2.37",
+	"version": "4.2.38",
 	"unity": "2018.3",
 	"author": {
 		"name": "Esoteric Software",