Adam,

 

I think something is changed by accident, because I still can reproduce the problem with your updated online sample.
Open that page, go to the first editor, select the option "Green Bold Text" in the richDropdownbox "CssClass". You will see that nothing will be added to the editor. The same code works before we upgrade from version 6.1 to 6.3.

Can you please try it again!

 

Thx,