Mail not getting all messages from Inbox

I get my email via Gmail using POP. For several months I have noticed that I can only download about 11 messages at a time, even if more are on the server. I have to rehit "Check mail" button until I get them all. It is rather annoying and sometimes leads to me missing messages that should have been downloaded. I cannot figure out how to fix this. I went to the Genius Bar and they could not figure it out. I have trashed the prefs files and that does not help. If I set up a new User it works fine, so clearly there is something awry in my User account or Mail folder, but I have too much organized and setup in Mail to just start afresh. Any help or advice would be much appreciated. Thanks.

p.s. This happens no matter the ISP I am on. I travel and it is the same everywhere.