After updating one of my sites to the latest version of WordPress the visual editor started acting odd. When I hit enter to create a space instead of putting it added in the previous div tag. So if I had div class="whatever" it added that in instead of a space.
I also just created a new subdomain and installed a fresh copy of WordPress. No plugins activated, Twenty Eleven Theme. It is not adding in whatever the previous div was, but instead it is not adding in anything when I try to put spaces in using enter.