This has happened to me twice, so I don't think this is a glitch anymore.
Today, 7/30, checking in at LAX for my flight to PHX UX 6520, I am given a DM card by GS check-in, even though I had reserved seat 8C when I purchased my ticket on united.com on 7/28.
The agent did not think I had a confirmed seat when I purchased my ticket. I did not have a chance to print out my e-tkt, but I did have a screen snapshot, which I showed her, clearly confirming my seat assignment.
I had a great check in agent, and she ultimately got me my seat back (someone else had taken it) after about 30 mins of phone calls etc.
I called the GS Res. number, and they said they would have to check with web support...they also did not show my seat as being pre-assigned earlier.
I am wondering why this is happening...I have a gut feeling this is because of OLCI, and for some reason they are giving my seat away.
This very same thing happened to me back on 6/1, going from SFO-RNO. That time, things weren't so nice. The check in agent and then her supervisor in SFO argued with me for half an hour, saying the reason I got a DM card was because:
1. I did not reserve a seat when I booked.
2. I did not purchase online (what does that have anything to do with it?)
3. I should have checked in 24 hours before online.