app not responging while frameless with transparent background and dragging to another screen with different scale

I am using frameless widgets with transparent backgrounds
this->setWindowFlags(Qt::FramelessWindowHint);
this->setAttribute(Qt::WA_TranslucentBackground);
but while dragging the app window to another screen with different scale (one screen 125% the other 100% on win 10 64bit) the app stops responding. it seems to be cycled in resizing. When I do the drag and drop very fast, it makes it trough, but with normal dragging the app stops responding and crashes. I adjusted one of the qt examples so you can debug it more easily In the example the drag is inside the the widgets