If you go to http://pics.livejournal.com/manage/pics?gal=##, you get the pictures in the specified gallery. If you select a picture or two and then go to the drop-down at the bottom and select "New Gallery", it'll give you a box to type in. So, let's say you type in the same gallery name as the one the picture is already in. One would expect that one of three things would happen: a) an error would come up saying "uh, no.", b) a new gallery of the same name would appear, with this photo in it, or c) nothing happens, as you just tried to move the picture to the same gallery it's already in (this is consistent with the behavior if you try to move a photo to a "new" gallery that has the same name as one you already have).
However, none of those things happen. Instead, the picture vanishes from the gallery it was in, and...it's nowhere to be found. There's no new gallery, and it's not "unsorted" either. It seems to have vanished into the vast space that are the pics.livejournal.com servers.
So yeah. Not a very good bug to have. :)