MouseMoveEvent working on Linux, but not on OSX

Hi, I have a program which takes heavy usage of the MouseMoveEvent for Mouseover highlighting in a OpenGl scene. The program runs with Qt 4.8 fine on Linux, Windows and OSX. Now, I ported the Linux and the OSX version to Qt5. The Linux version works still as aspected, whereas in the OSX version the MouseMoveEvent is not excuted when moving the mouse without pressing any key. I didn’t use any Eventfilter, with Qt 4.8 it was enough to simply set Mousetracking to true. When trying it with a simple example on Qt5, again the setMouseTracking(true) command is enough to let it work. Therefore, here is my question: How can I check if the MouseMouveEvent is spawned and/or why do I see nothing. Properly I would like to have some suggestions for debugging. Thanks for your help. Mike