yahoo mail showing twice

My yahoo emails show up twice in my messages occasionally. It's not every time either which makes it more confusing. For instance today in my yahoo I have the following emails if I check online:
sporting news
buy.com
investments
gold buyers offer
gold buyers offer

But if I check my email on my BB
sporting news
buy.com
buy.com
investments
gold buyers offer
gold buyers offer
gold buyers offer

So I received 2 "buy.com" messages (despite 1 in my yahoo account) and 3 "gold buyers offer" (and had 2 of these in my yahoo account), but 1 of the others.

Any ideas? (running version .90 if that helps).

I think it's a Yahoo server thing. I use YPops to check it from my desktop under windows live mail and occasionally it does the same thing. It downloads duplicates. I know this is discussed in the YPops forums but haven't looked into it as it doesn't happen that often. I would suggest doing a search for it and see if there is a time out or server setting you can fiddle with.