CKEditor is not 'full' ready for HTML 5. CKEditor's developers working on it but this takes time.
Well, yes of course. As HTML5 is still a draft that wouldn't be possible anyway. But I don't think it's a sustainable solution to force this HTML 'correcting' as the language won't stop developping and the validator will continue to lack behind.
In general it is designed for HTML 4.
Ah, ok, I didn't knew about that. It's advertised as being a rich text editor.
Please remember that CKEditor is made for 'everyone' not only webdevelopers. So it should be easy to use by all users.
Well yes, that's exactly my problem. I don't need the CKE, I have it installed solely for my client so he can edit content I wrote. But as it is, he can't do that without messing things up.
Honestly I believe a validation on/off-switch would be a prerequisite for an editor that is made for everyone.