Been working on this client's site, and they just pointed

Hi! Been working on this client's site, and they just pointed out an issue.

They're saying it wasn't a problem until I changed the width of her site. Not sure how I could have created this, but happy to fix it if I can figure it out.

So if you look at this post here: http://sadieraeandco.com/2013/10/23/redhead-halloween-costume-ideas/

She's using a standard WP gallery here, set to "Square Tiles" but the formatting is getting thrown off. If you inspect element, you can see there's an extra div being created every third thumbnail.

Weird right?

Can anyone help me solve?

THANKS!