"Simple Blog", "Simple Event Calendar", and "Simple Button"
None of them messes with CKEditor configuration, so I'm a bit clueless where the come from.
Do they already exist when you switch to "Source" mode in CKEditor right after you input some text (don't think so).
So here's some guesswork:
- Do you have HTMLtidy installed on your server and enabled it in Typesetter Configuration? If so try to disable it.
- Maybe also try different browser (FF 60 was still shortly after their "Quantum" overhaul and I remember it had some minor bugs then, but nothing you encounter)