That explains it. Though I am not sure if the agent actually made a mistake.

Last year I had an award one-way IST-LHR-MIA-LAX. The date of departure from IST was May 15 with an overnight layover at LHR. Either leaving on 5/15 or 5/12, I had no choice but took the 5/15 date. Agent insisted it was 30K. I reminded him departure was 5/15. He balked saying not only the LHR-MIA was 5/16, but MIA-LAX was in Summer. I politely asked him to please check with rate desk so neither he or I would get into trouble. He came back said it was 20K. He kept saying that he could not believe it... and ticketed it at 20K.