It's one of the annoying things in the forum's software - search for Dumbledore and you'll not be able to find him either
. There are quite a few words that the software has automatically identified as "common words" and which aren't searchable on. I've recently been intending to look into whether going through the word-list and re-identifying many or even all of the words as non-common would cause any problems but haven't been able to look into this yet - 'tis something I'll certainly look into soon though.