Found an interesting bug.
If a member group only has access to one weblog and they click the “Publish” tab without selecting the weblog listed beneath, they get a new publish form assigned to that one weblog. When a weblog with a lower weblog ID than the one the author has access to has a different (non-“Publish”) tab set to be “forward” in Tab Forward, then that setting gets applied to the weblog the member does have access to.
If they do select the weblog listed in the dropdown this doesn’t happen, only when clicking directly on the word “Publish”.