My seat assignment changed from 9A to 11C after OLCI for a p.s. flight earlier in the week. When the BP reader chimed that I had a seat change, I told the gate agent that I had specifically chosen 9A, but would happy to move up to F if it was no longer available.

I was told First was full or I would have been moved up. The man in 9A (probably moved up because he literally weighed ~500 lbs) was promptly moved to 11C.