Of course I've been up all night! Not because of caffeine, it was insomnia. I couldn't stop thinking about coffee.
In the sense that you can search only once per tile does the other side count as the same tile?
It's best to think of it as one successful search per mouse per room.
It's also best to have it written that way in the rulebook, but it's too late for that.
I like to use poison hearts on the initiative cards to remind us who's been successful. Unfortunately there's no way to track this if you leave the room and come back... so we just don't allow searching on subsequent visits.