I was flying UA PBI-EWR and boarded with Group 2. Towards the end of boarding a lady approached me and told me I was sitting in her seat. She showed me her boarding pass and I was surprised to find her holding (a duplicate of) my boarding pass with my name, frequent flyer number, reservation and seat. Not only that but it was signed off on by TSA! A flight attendant said she has never seen anything like that but found the lady a different seat. I emailed United expressing my concerns over how my boarding pass could be issued to someone who clearly wasn't me (we both had passes printed by the agent in the airport), how TSA could sign off on it when they check it against an ID, and how the gate agent boarded her if my boarding pass was already scanned in. I got a call back from the executive offices saying they alerted the station master and the TSA station in PBI and would investigate, she did mention that she pulled up the boarding register and saw that my boarding pass was scanned in twice.
They also gave me 10k miles as a "goodwill gesture".
