This probably won't help... but
I have a number of sites that sit on a single DNN platform (currently at 9.11.00 (46)) also all of the sites are using variants of a skin (that allow different colours) but essentially same. 2 of the 28 sites have an issue with the editor in that they will not display the WYSIWYG icons etc. I have to edit in another portal and copy the formatted text across as Source.
My sites are effectively "out of the box" with two modules, the included Reports module and the purchased Datasprings Dynamic Forms (which is brilliant) the latter also exhibits the inability to show the RichText format if I use the HTML option for a question..
I've also checked to make sure that permissions for the editor are not restricted the number of icons, but this does make me think I wonder if there is some hidden setting somewhere that is overriding local.
I'll see if I can run something in SQL that may expose this :-)
Now you have forewarned us I will follow best practice and do some offline tests before upgrading in a live environent, although I can replicate my platform on the same live environment and assign a number of portal alliases to run a "live" test.
If you find the solution / cause please share :-)