I ran into the guys in the cave and helped them beat the Gnolls. Then I stealth opened the Chest and took what was inside. When I went to the Barn and entered the hideout with the password nobody knew I had opened the chest. Not sure if that was a bug or what.
It's not a bug. It changes what's going on inside the cave. You'll get a chance to tell on yourself and the Zentharim will respond accordingly.
Edit: I decided to not only steal the content but snatched the entire chest during the fight, so might have a different scenario on your hands.
