POP mail reader suddenly gets duplicates

Twice this last week my POP mail reader (Apple Mail) would all of a sudden download duplicates of several days of e-mail. No big deal. But I’m curious if it’s on my end or DreamHost’s end.

The duplicates coorespond to my settings of how long I wait to delete mail from the server. So what is happening is all of a sudden all the mail on the server downloads again. Not knowing the protocal, I can guess there must be some sort of counter keeping track what has been downloaded that must be getting reset.

It happened sometimes today, maybe in the last hour.
Earlier in the last couple weeks it happened when I asked DreamHost support to fix a permission problem on a mail folder.