Many times in the game, I'll see a lair with a green "Notable Location" HUD icon instead of the appropriate purple Lair HUD icon.  I've seen it with Ruffian Camps (although I'm not sure they count as lairs), Great Wolf Dens, and in the screenshot below, Brood Lair, which actually has the word lair in it.

I'm not talking about after you've cleared it out.  No, it's still occupied.  Those guys aren't moving.  I know a lair will turn into a Notable Location once it's been cleared (sometimes, not all the time, which I guess is another bug), but these are starting out as Notable Locations, not turning into them.

I could provide a save game, but I have yet to play a game where I haven't seen this problem early on.  Start a new game with Dense monsters.  You'll probably see one in the first 10 minutes.

It's mostly a problem for determining:
1. Will the monsters on that tile move from it?
2. (When that tile is covered by the fog, so I can't see if there's a monster on it...) Is there a monster there, or is that just loot waiting to be claimed?
3. (This one shouldn't actually be a notable problem anymore in .80 due to +1 city sight) If I have a city whose zone of control now borders that tile, will expanding my borders from building a Town Hall release a monster that may destroy said city?

I've noticed this bug in all versions of FE I've played, I just never bothered to report it as a bug before. I've been meaning to, though.