Stuck with jquery Masonry

Stuck with jquery Masonry

I'musing a javascript called Masonry ( http://desandro.com/resources/jquery-masonry ). I'm using it for my new Tumblr blog. http://thingswelove.tumblr.com/ But their is a very strange bug I don't know how to get rid of. If I load the page for the first time the post aren't nicely stacked, but flow over each other. But when I reload of resize the page looks fine. It is mostely the problem in IE7 but also in firefox it sometimes goes wrong.

I would really appreciate if somebody could help me out.

Cheers,
Mathijs Alderliesten, The Netherlands