And just to confuse things, there is a bug whereby a dungeon is generated empty! <img src="/ubbthreads/images/graemlins/puppyeyes.gif" alt="" />
So you might find a 'new' dungeon and still discover that it's empty - and assume that you must have cleared it already.
When this happened to me I could pick the problem as there were still items in barrels etc and no signs that I'd been through before (i.e. no rejected junk lying around) just no monsters at all on all 3 levels.
