Category page 2 displaying unnecessarily

I have a Category filter widget on my site (www.retrosmackblog.com). When someone clicks on a category, they are taken to a page that shows only the posts that have that Category.

The problem is that even though I’m displaying 12 posts per page on the site, and none of the individual categories have more than that number in them, readers can always see a Page 2 option at the bottom of the screen. If they click on it they understandably get a 404 error.

I’ve read stacks of posts online where a similar thing happens to other sites, but in every case it is happening when people do actually have multiple pages of posts to display. In most cases they’ve resolved it by making their archive pages display the same amount of posts as their site default, but I’ve not mucked around with that on my site.

Any idea why Page 2 is appearing?

Thanks,
Tricky.