diff --git a/spine-as3/spine-as3/src/spine/animation/FfdTimeline.as b/spine-as3/spine-as3/src/spine/animation/FfdTimeline.as
index 1f9c323ea..532a1c799 100644
--- a/spine-as3/spine-as3/src/spine/animation/FfdTimeline.as
+++ b/spine-as3/spine-as3/src/spine/animation/FfdTimeline.as
@@ -66,7 +66,7 @@ public class FfdTimeline extends CurveTimeline {
 		var vertexCount:int = frameVertices[0].length;
 
 		var vertices:Vector.<Number> = slot.attachmentVertices;
-		if (vertices.length != vertexCount) alpha = 1;
+		if (vertices.length != vertexCount) alpha = 1; // Don't mix from uninitialized slot vertices.
 		vertices.length = vertexCount;
 
 		var i:int;
diff --git a/spine-c/src/spine/Animation.c b/spine-c/src/spine/Animation.c
index 755da5738..e4f261eed 100644
--- a/spine-c/src/spine/Animation.c
+++ b/spine-c/src/spine/Animation.c
@@ -664,15 +664,15 @@ void _spFFDTimeline_apply (const spTimeline* timeline, spSkeleton* skeleton, flo
 		return; /* Time is before first frame. */
 	}
 
-	if (slot->attachmentVerticesCount == 0) alpha = 1;
+	if (slot->attachmentVerticesCount != self->frameVerticesCount) alpha = 1; // Don't mix from uninitialized slot vertices.
 	if (slot->attachmentVerticesCount < self->frameVerticesCount) {
 		if (slot->attachmentVerticesCapacity < self->frameVerticesCount) {
 			FREE(slot->attachmentVertices);
 			slot->attachmentVertices = MALLOC(float, self->frameVerticesCount);
 			slot->attachmentVerticesCapacity = self->frameVerticesCount;
 		}
-		slot->attachmentVerticesCount = self->frameVerticesCount;
 	}
+	slot->attachmentVerticesCount = self->frameVerticesCount;
 
 	if (time >= self->frames[self->framesCount - 1]) {
 		/* Time is after last frame. */
diff --git a/spine-csharp/src/Animation.cs b/spine-csharp/src/Animation.cs
index 2fdbebc5d..112a445a5 100644
--- a/spine-csharp/src/Animation.cs
+++ b/spine-csharp/src/Animation.cs
@@ -580,7 +580,7 @@ namespace Spine {
 			int vertexCount = frameVertices[0].Length;
 
 			float[] vertices = slot.attachmentVertices;
-			if (vertices.Length != vertexCount) alpha = 1;
+			if (vertices.Length != vertexCount) alpha = 1; // Don't mix from uninitialized slot vertices.
 			if (vertices.Length < vertexCount) {
 				vertices = new float[vertexCount];
 				slot.attachmentVertices = vertices;