I'm pretty sure that the MAV_BLOCK missing has other causes as well. In a project i'm working on, mesh is generated, and if there are multiple materials/colors, they never share the same vertices, they are always different pieces of mesh. So for me, that can't be problem, but sometimes I get the error anyway.
Also in the only jira entry about this error (as was mentioned earlier here: https://jira.secondlife.com/browse/SVC-7823) the error does not seem related to materials sharing vertices, but rather there might be something wrong in the physics calculator.
So I'm not saying that the problem you've described is not a cause, but there is certainly also another cause as far as I can tell.