How to avoid the TrackBar flicker

[cae]

Hi,

When a trackbar is made visible in a parent window, it flickers,
showing first a rectange filled in gray and then the actual trackbar
(with a white background because I want so). If I later resize the
trackbar control, it redraws correctly without flicker.
Then, if I hide it or move it outside the window, and show it again or
move it inside the window, the flicker happens again.
I tried to derive it and play with backcolor, OnPaintBackground, ...
but nothing works.

Thanks for any idea you could have.

Herve