Hi there,
I have got an issue with CKEditor 3.5 (haven't checked earlier versions) with the option enterMode set to CKEDITOR.ENTER_BR.
1. In the empty WYSIWYG editor, type "test"; the generated HTML is "test"
2. Delete the text in the WYSIWYG editor by any mean (pressing backspace, delete, Ctrl+X, it does not matter)
3. Type "test"; the generated HTML is
<p> test</p>