It happens to me as well... and I also think it's not a consistent problem (sometimes it returns to the expected place, sometimes to the search box). I haven't spent any time researching it due to minimal impact to operations of the forum. If I dig and research the problem, I'll post what I find.
Ken Grammer Used Snitz on SpecRacer.com and GT_RaceCar.com
Well then a few more facts. This was a brand new forum install, no mods. One user added as a test account. After modifiying the user name and password (with the admin account) and clicking Submit, the search box appeared. Happened twice in a row, then could not duplicate the problem.