This would be too big a bug to not be on Google, one would think.
Repeatable problem. (click) Start -> (click) Search -> (click) Pictures, Music, or Video -> (check) Pictures and Photos -> (type text: testing) All or part of the file name -> (click) Use advanced search options -> !! "testing" has now been moved from the "All or part of file name" field to the "A word or phrase in the file" field." !! This happens every time. (I finally stepped through this as my image searches kept searching inside of files instead of for matching file names. I thought at first I kept putting it in the wrong field, but I couldn't have been, as that field hadn't even appeared yet.)
Windows XP SP3 w/all updates (updating is enabled).