I found that I was still getting the issue described here - http://www.question2answer.org/qa/16886/strange-issue-with-ip-addresses
Some users' last write IP shows my IP address. The approve/reject thing was fixed but it was still occurring. I've just figured out that it occurs when I run the "Delete hidden posts" in Admin > Stats.
It just deleted about 100 comments, 50 answers and 50 questions and now there are 8 users with my IP as the "writeip" and with the "written" field as the time I deleted the posts. That can't be all the users who had deleted posts. Maybe it's just users who recently had posts rejected?