I am playing around with your site and am wondering if this is due to a sort preference?
For example, when I click on your link, I see the Sweet Pea, but if you look at the sort preference of the linked page in your message, it is sorted by A-Z.
When you click on Page 2, it's sorted by Default making the Sweet Pea pop up again.
If you select sort by A-Z on Page 2, the Sweet Pea is not there anymore making me think that the Sweet Pea item was added earlier, but the sort preference is changing when you click from Page 1 to Page 2 making it look like the items are duplicated when they probably aren't.
If you keep using the same sort preference, the items don't seem to duplicate anymore.
EDIT:
Hmm, playing around with my site, I think the "bug" is that if you sort by a preference OTHER THAN default, clicking on page 2 puts your sort preferences BACK to default causing some display problems to pop up.