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Copy Location Bone Constraint on Vertex Group does not work with Subsurf
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In 2.60 and 2.60a adding a Copy Location or Child Of bone constraint to a vertex group on a mesh doesn't work if the mesh has a Subsurf modifier. Strangely if you add a Mask or Armature modifier after the Subsurf it behaves as it should.

In the attached file the bone has a copy location constraint on the Vgroup of the cube. Make visible the Subsurf modifier on the cube and it no longer works.

If you make visible the Mask modifier it works as expected.

CPU: Core i5 760
RAM: 8 Gb
GFX: GTX 460
OS: Windows 7


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I can confirm this also with the older r39294. I noticed it a while ago, but forgot to write a bug report. really a little bit strange.

Well, it seems like blender tries not to interpolate vertex group if not needed.

You can be more precise at restoring bone location if you choose a Vertex Weight Edit modifier.

This is a case that the dependency graph can't handle yet, the constraint needs the vertex group to be preserved by modifiers, but it has no way to specify that at the moment. It will not do this by default because it has a major performance impact, the mask modifier works around the issue because it will request the vertex group to be preserved.

Brecht, is there something we can do here or this cn be moved to our TODO?

I've added this to the todo list now: