QSplitter doesn't propagate style sheet on QPushButton

[desch]

Hi,

I'm experiencing a strange behaviour with style sheet and QSplitter. In the following attachment, you can find a full project containing different QPushButton at different place. All of them have a dynamic property ("toto"). The CSS file just styles all "toto" properties. For QPushButton outside the QSplitter, it works. But for those installed in QGroupBox and then on QSplitter, they are not styled at all.
This can be reproducible with Qt 4.8.6 and Qt 5.4.
So, what's the problem? a bug, something I did wrong ...

Thanks a lot for your help.

David