Weird Layout problem

[gprit]

In the late stages of setting up store with over 1800 products and there appears to be a random 'wrong' layout (see attached) - no pattern to it that I can see. Other products are ok.

Have checked the template/database etc and all looks fine. The strange thing is that if I go into admin, find the product and just hit preview and update, it corrects itself.

Has anyone else come across this - and what causes it??!

thanks