When managing users from the ACP, clicking the Find a username button sometimes does not bring up the dialog box for finding a username, but Sorry, but that user does not exist is now displayed on the main page. When the dialog box does pop up and you do your search, selecting a username has no effect and Sorry, but that user does not exist is still displayed on the main page.
This bug exist on my 1.1.0.15 board and here on Icy Phoenix as well.