watch, then I would think there may be an issue.
When I set my watch, I sometimes wonder if I am getting the moon centered correctly, then counting the proper number of days to the correct day and for the most part, it seems to line up pretty close to how the moon appears in the sky.
There have been occasions though, where I had a similar experience as you but I may have not set it correctly. With my 5015, the moon phase can be set precisely and I can get that set pretty much on the money every time.
I would try re-setting the moon-phase again to see if you experience the same thing.