Product count reduces when I click on next Page

Hi,

I see a bug but I am not sure if it is an opencart bug. Please check http://citycarts.in/shop/women/saree and attachment 1, Initially product count is 717. When I click on click on page 2 or any other page (http://citycarts.in/shop/women/saree#/s ... =20/page=2), the product count reduces (please check attachment 2) and some of the products displayed earlier in page 1 disappears on navigating back to page 1.

Why would this be an OC bug and not a custom theme bug?