Placement help

Please, please, please could someone cast their eye over this and let me know what's going wrong? 

The fifth square is overlapping with the fourth when it's clicked on for some reason. I've looked at the different states and they all seem to be placed ok, I've tried deleting and re- adding it and I've tried duplicating one of the others to use instead and it still happens every time. I must be missing something but I really can't see what and it's driving me mad!

Thanks!