Problem with CSS style "float"

I'm having an issue with using any float options in CSS. As soon as I add float:left or similar to any content, the view is incorrect. The alignment itself works as expected, but the content-divider (grey line which can be found under each content) lies under the contet suddenly. See the image attached.

Without the float-tag, everything looks perfect. Any idea how to fix this? Thanks!
I'm not sure whether its a bug or I am just missing somethin...
-astein