I also had a UA e-ticket EWR-SEA pulled out of order flying with a connection in SFO on a rare domestic trip at the dawn of e-tickets. The initial segments were 1-2-3-4, and on beginning my return trip, the computer showed x-2-x-4 (segment 3 was pulled instead of 2). It took about 15 minutes or so for UA to straighten out the mess.