Oh, okay !
So now I know some ideas I had weren't possible the way I thought them. I'll try to call some functions or to rethink my design, when possible, and when I need such behavior !
Nowadays, I use exec(), and sometimes show() followed by QCoreApplication:rocessEvent() when it's possible.
Maybe I'll come to this later on this topic (maybe not, depending on the time I have), thanks for your help !