I stopped by the United counters at PHL this afternoon to book a couple tickets and happened to pick up on a conversation to my right as the agent assisting me was trying to figure out how to book a ticket (it had been a few years, she claimed).
A man walks up to the Economy check-in entrance and a UA employee directing passengers to open kiosks asks him where he is traveling to.
PASSENGER: Los Angeles.
UA AGENT: We don’t fly to Los Angeles from Philly. You must be on US Airways.
PASSENGER: I’m pretty sure I’m on UA.
UA AGENT: Let me see your itinerary. [man was holding a printout in his hand]
PASSENGER: Here. See?
UA AGENT: Hmm. Sure enough.
Now this was not a contract agent (he was wearing a UA uniform unlike the contract agents at PHL) and he did not appear to be new to UA, based on the pins he was wearing on his sweater.
Apparently UA849 must be a phantom flight.