Both tries work well for the first selections and the updateSelectedFacesMouse-method is called every time. After some time/after some selection or a rotation the method is not called anymore. I think there must be a kind of "recalculation" of the ModelViews? Is there any event for it to get the correct mouse-object afterwards?
I dont know why, but after I opened the thread everything works fine. And I found the Event "ActiveViewChangeNotify" of PartDoc and I hope this will solve the problem for the future. For know I would check my question as "answered"