Comment 7 for bug 1070008

OK, so this check is failing. dynamic_cast<>() is returning null because this is being called from the constructor, and the vptr during this stage of construction does not contain the information about the derived class. So we end up setting the mount device inappropriately.

This was working previously. I can only assume that this is a change due to a GCC upgrade, though it appears to affect both 4.6 and 4.7.

The code is definitely not following the letter of the C++ standard, so it will require refactoring to remove this logic entirely.