Just had an interesting call from UA regarding two farelocked itineraries for the end of the month - one departing Feb 27, one departing Feb 29 for LHR from ORD - both with same return date of March 4. United forced me to cancel one of them and said that their system saw them as duplicates. I said they obviously aren't duplicates as I don't know which day I am leaving yet - they didn't care and didn't want me tying up inventory. I have been farelocking like this for years - first time I've had this happen - just good luck or is this new?