in every page generated in the cms. this error happens for example when you write the title of a new page and press enter (to publish the document) instead of tab (to go to the next field in the new page form)
But there are three submit buttons at the base of the admin. Noone ever said that pressing enter activates the "Save" one. Infact, I'm not sure what a browser's default behavior would be with multiple submit buttons on a form. But I imagine it would differ between FF and IE.
Is this functionality really all that critical? I don't think you can expect a user to assume that pressing enter Saves a page. At least I wouldn't. They might assume that it Saves and Publishes.