I tend to book our Hawaii trips (we've been many times and lived there too) very far in advance using airline miles.
With both Delta and American this has happened. I booked our next trip this summer last fall on AA, and it changed twice. Worked out to my benefit, though! We booked first class both ways, and the outbound had us stopping twice (not ideal), so they were able to change it with only one stop and lie flat seats instead!
I check the flights frequently, as sometimes I'm not notified of the change. It can happen with any airline when you book so far in advance.