I have to add "QMAKE_CFLAGS = -m64 -fno-strict-aliasing" to the mkspecs/linux-g++-64/qmake.conf and rebuild Qt. Thereafter it runs much more stable. The problem is reported by many people on the official Qt bugtracker. I know its a workaround for legacy code, but I really like to see my QML apps run with default Qt libraries. Best wishes, Frank Mertens.