Some time after clearing Gallows Rock as part of the Companions questline, I accepted a radiant quest from Jorleif to kill a Bandit Leader at the same location. When I arrived to do the quest, I found the entire fort populated with Silver Hand members instead of bandits. There was even a brand new Krev the Skinner, who happened to be flagged as the bandit leader. Killing her completed the radiant quest, and didn't affect the Companions questline as far as I can tell.

So, not really a game breaking bug, but a glitch none-the-less.

Has anyone else encounteded this?