@d-healey Just my stupidity that knocked at the door... again...
I was drawing the value of my vector knob in the panel via paint routine so everything is handled in one panel. But today I wanted a label that is set visible for typing the new value manually... So I just had to remove my painted value and replace everything by a label... Much easier than going back and forth between painting value, unhide a label for typing, repaint, etc...
So finally, stupidity knocked, wisdom did not open...