Comment 3 for bug 682327

Actually, the bug is crashing compiz rather than X.

It sounds like when doing alt-tab, to draw the dialog compiz is passing in a GL format that mesa doesn't support. _mesa_format_to_type_and_comps in ./src/mesa/main/formats.c is basically just a big huge switch statement for every possible texel format, which is used to generate mipmaps. In this case, it is getting to the end of the switch statement, where it hits the default, which is to issue the format error:

      _mesa_problem(NULL, "bad format in _mesa_format_to_type_and_comps");

So, we need to know what format compiz is passing in.