This is caused by the code used to start output for version checking on ACP home.
That in mind, this specific manifestation only occurs if there is only 1 user in your forum's database that matches the selected criteria, because instead of listing 1 search result vBulletin figures it might as well redirect you to the edit page for that user.
In any case, I added a check to prevent the output start for version checking unless we are on a page that can show the results of the check.