Broken layout

As seen on the page http://www.hohenberger-wallcoverings.com/showroom/ the 3 column layout is not displayed the right way – sometimes it breaks after 2 columns or leaves one empty – when I increase the min-height for this columns in CSS it would work and display the 3 columns in each row but that doesn´t look so nice anymore and so I hope you have a better solution for my problem.

Do you need access to the backend to solve this problem? If yes, please tell me an email adress to generate an account for you.

Thanks for your help!

Kind regards,
Jessica