The user requests a temporary password by email, enters it, and then enters their desired password. They receive a success message from Special:Resetpass, and then a failure message from the login form which executes via FauxRequest during the same real request.
Can't reproduce locally, probably erratic. Not sure why it happens, but obviously avoiding the SELECT query in LoginForm and using a cached password instead would avoid it.
Version: 1.15.x
Severity: critical
URL: http://img518.imageshack.us/img518/2615/passdj5.png