how to preserve background after invalidate?

[Rupel]

hi, i'm doing some rect-invalidate-update-paint things. it works quite well with one exception: the painting process is flickering, because the invalid rectangle is filled with the background-color first. does someone know, where i can turn that off? i'm relatively new to C# and that class library. i hope it's just a matter of finding the right property... thx in advance :) :wq