Hi Margrit, we have seen the exact same situation. When copying a screenshot from another source, it seems some of them work and others do not. You only discover this after you save the article and then preview it. While I do not know what causes it, our solution has been to capture the image as a screen shot. This seems to work consistently for us. We use snag it as our image capture tool. It's a pain, adds more time to knowledge creation, but there you have it. Another workaround for knowledge management.
EDIT: how ironic that I clicked on this known issue next and all of the screen shots in it are broken. It gave me a little laugh this morning.
