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I had seat assignment problems on all four legs of my flights in the past two weeks that even numerous phone calls didn't solve. Every time I checked back on line, I had been moved to the rear of the plane. Only one (first) leg was on CO metal, though, and the rest were on UA or UA Express. Once I had done outbound OLCI, the first two segments stuck.

On the return I couldn't choose seats on line, so I went to the UA(ex) counter when I dropped off friends at the airport the day before. The UA counter agent apologized and rolled her eyes saying "And they(?) keep telling us we're getting there." After typing for a few minutes, she printed boarding passes with the seats I requested and told me not to lose them. She also had to add me manually to the standby upgrade list.