Plumiferos report:

Bad bad bug in Vector Blur: when using Ztransp in a RenderLayer,  the speed
vectors of moving solid faces were all cleared. Bug since january 21st... is
this the 2.43a case? Dunno... :)

source/blender/render/intern/source/zbuf.c

@@ -2977,7 +2977,7 @@ static void reset_sky_speedvectors(RenderPart *pa, RenderLayer *rl)
 	
 	fp= RE_RenderLayerGetPass(rl, SCE_PASS_VECTOR);
 	if(fp==NULL) return;
-	col= rl->rectf+3;
+	col= rl->acolrect+3;
 	
 	for(a= 4*pa->rectx*pa->recty -4; a>=0; a-=4) {
 		if(col[a]==0.0f) {