Thread:Project:Support desk/New user is always attributed to next edit in 1.18.1?

Some disturbing behavior in my mediawiki 1.18.1 installation (PHP 5.2.9, Mysql 5.1.30). Closed company intranet (no link, sorry).
 * 1) I create a new user and assign them some groups.
 * 2) Another user makes an edit on some article.
 * 3) The article edit is attributed to the new user!!!

Only happens for the very next edit after user creation. Looks like it's been happening since upgrading to 1.18.1 (couple years ago?). Never noticed it till one of my users watching a particularly important page was wondering what newuser was doing messing with it already! Is this a recognized glitch? Seems to only stick for very next edit. After that, everything is fine. Panic!