HELP: Weird behaviour by TImage and TImageList!

I have large amount of images stored in a TImageList object and I want to
show one of those images in a TImage object. When the programme needs it, I
want to swap the image in the Timage object for another image from the
TImagelist.

I try to do it like this:
MyImageList.GetBitmap(SomeNumber,MyImage.Picture.Bitmap);
MyImage.Repaint;

But when it executes this code the old and the new image seem to be drawn
through eachother. Has anyone some idea how this happens and how to avoid
this? Please reply to my e-mail address 'cause the NG Server deletes the
postings too fast.

Greetings,
Francois H. Reincke