While not simple to show an example, behavior was noticed as follows since upgrade to 1.18.1:

1. CategoryWatch extension is enabled (either version 1.2.1 or 1.2.2)
2. A new user is created.
3. A different user saves an edit.
4. History indicates the new user (not the editing user) is who made the edit.
5. Subsequent edits behave normally (it only happens for the first edit after creating new user)

Have since upgraded to MW 1.21.2/PHP 5.3.10-1/mySQL 5.5.32-0.
Behavior remains.

Identified CategoryWatch as the contributor by disabling all extensions and activating one at a time, creating a new user and performing an edit with another user.

Very weird. Will try to duplicate on a test installation.

Version: unspecified
Severity: normal