when creating a screenshot I realized a problem in Xnview I never had in IrfanView (which I used the last years). To describe the problem there are 2 screenshots which I took from yahoo.com with IrfanView + XnView. The problem should be very clear when comparing both screenshots - it should look like the one taken with IrfanView. The preview after taken the screenshot was ok, though. When I saved the screenshot as a gif, obviously something went wrong.
Screenshot taken with xnview:

screenshot taken with IrfanView:

Gif-Settings of xnview:

What went wrong?
Thanks for any support!
Thorsten