8-bit bitmap turns into 24-bit bitmap

I want to copy a 8-bit greyscaled image to the clipboard.

if image1.Picture.Bitmap.pixelformat = pf8bit then
  Clipboard.Assign(Image1.Picture.Bitmap);

This works, but when pasting it from the clipboard to another
application such as Paintshop Pro, is is pasted as a 24-bit bitmap.

To be shure that this is my fault, I copyed a greyscaled bitmap in Corel
Photopaint, and pasted that in Painshop Pro. This did work right (was
pasted as 8-bit bitmap). So what am I doing wrong?

Thanks in advance,

Louis