I have been doing some tests and it seems I was partly mistaken. Deltatime and the timer itself ticking are not changing (I still fail to understadn why the timer is forced to 75 ticks a second when I set to vynyc but...)

The problem now is: In window mode time based with vsync, the ball is not running right speed if I cap the deltatime to say 17 (then I force it to have 17). In fullscreen mode, the ball jerks more but still matches the speed that was set....

I am thinking simply, that fullscreen mode means my game is able to run much faster but I cant be sure....I will send a demo some time i guess