controls repaint delay

Question

i have built a winForm wich has buttons, textBoxs fields and a calendar control. when i click one of the buttons another winForm opens on the first winForm. now the problem is when i close this last winForm : - all the controls on the first winForm that where under the last winForm (like the buttons and the calendar) are being repainted, but there is a kind of delay and for some microseconds i can see on those controls some leftovers from the last winFrom. how can i cancel this sluggish control repaint ?