Possibly a TincMCE problem. When you mark the second level list as greek alpha then it shows up as greek alpha. Open "View source" and you won't see any related CSS classes which I would expect here. Close "View Source" and the greek alpha has gone...so it appears like a complete client-side problem and I would possibly blame TinyMCE here.
I wonder why HTML filtering takes place client-side too...this was always a server-side only functionality?!
Anyway...when you disable HTML filtering completely then the TinyMCE shows the dedicated CSS class and the content can be saved and displayed properly (tested with Plone 5.1.2.1 on plone-demo.info).
It is clearly a bug or a bad plone default configuration for TinyMCE not defining the associated CSS attributes as allowed in the default HTML filtering settings -> please file a bug report for this.
Thanks Espen. Yes, before I disabled HTML filtering, I tried to add "type" as a valid tag and as a allowable custom tag and in both cases it failed. You are right. Only when I disabled filtering did it work. Thank you so much!
Epsen, this is awesome! Yes, I did exactly what you recommended and uncheck Disable HTML filtering while I was at it It is working perfectly! Thanks so much!!!