RebuildMesh not working like V5 - ExtractMeshPart

In Rhino 5 I could use commands like ExtractMeshPart with no problem most of the time, and when it didn’t work I could run RebuildMesh and then it would, but that doesn’t seem to help in V7 and I think it is b/c RebuildMesh has changed - I just did a test where I opened up a mesh I couldn’t get to work in V7 in V5, ran RebuildMesh in V5, then copied it via the clipboard to V7 and then ExtractMeshPart worked. Is there anyway to get RebuildMesh to work like it used to?

Hi Matthew - best to post an example mesh or send to, with a link back here in your comments.