A css problem ?

Hi, I’ve been developing my first theme, but recently I found a problem and I can’t fix it.

When I create a post without an image it shows like I want
(example: http://inove.ptbackup.com/dev/design/post-sem-img/)

But when the post have an image the “rullers” width size goes smaller.
(example: http://inove.ptbackup.com/dev/webdesign/criacao/post-com-img/)

I’ve been looking around the css but I can’t find any solution.
Did it happend with more users ?

Thanks