MinGW version of gcc - 4.7.2, bundled with Qt 5.0.1 has a very nasty bug, which may reveal when virtual inheritance is used. Details are covered here http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55171 . If anywhere in Qt app virtual inheritance is being used, then watch out, because program may crash or behave unexpectedly. It has taken some time for me, to realize that this wasn't my fault. Version 4.6.2 provided by MinGW manual installation (http://www.mingw.org/wiki/InstallationHOWTOforMinGW) is free of this bug. I'd suggest to downgrade to this version until 4.7.3 is released.