Booked a flight FLL-EWR-BOS-ORD-FLL. BOS-ORD is operated by United. There was a slight schedule change on the BOS-ORD flight, by approximately 11 minutes, and, when this happens, YOUR ENTIRE RETURN CANCELS! Thankfully, I checked into my account, saw the flights (and realized that they had disappeared) and the rep at the Elite Desk explained that this happens frequently and can only be fixed when you call in to confirm you are alright with the change. (however, I NEVER RECEIVED NOTIFICATION) I am glad I looked....on a separate note, you know how companions are cleared on the same day as the elite on UA? Well, I split the reservation I had (to clear for CO at T-72) and the upgrade still shows as "Pending" for my companion; glad it will still work!

Had something similar happen to me on a combined CO/UA EWR-SFO-GEG, due to weather on Sunday night, missed my connection to GEG, had the gate agent rebook me on the first flight out Monday morning as soon as I got off the plane in SFO. I go into my account Monday night and all my return flights were gone, including my FC seat to EWR from SEA which I then had to rebook on an earlier flight to get the FC seat back. It took multiple phone calls to CO/UA and finally get it fixed.