Image resizing does not work in "Twenty Eleven"

Hi,
I am using the “Twenty Eleven” theme, in wordpress 3.2.1, without any change of code or any plugin, and when I try do resize an image in a post with the built-in feature, the image stays full-size in the post.

Now the strange thing is when I chose another theme than twenty eleven, this feature work perfectly well.

I have search the forums for this problem but couldn’t find anything relevant.

Can anyone help me out ?

Thx