Hi Joerg,
Are you on the latest ListMail files (v1.87d?) Also are you using the mailbox method of bounce processing? I have heard a few reports of that process reporting and/or removing the wrong users, etc.
I don't see the bouncing users' email address in the bounce notification, which is a bit strange. You may want to try replacing your bounce.cgi (if you use it) with the one included in the most recent version, although that file normally doesn't change and hasn't in a very long time.
I will have to consider this more later today. If you want to submit a possible bug report you can
do so here - this will give me all the access I need to troubleshoot things.
If you want to attempt to gloss over the problem you might change your bounce email...
Regards