I'm always doing non-standard stuff and finding bugs. =))
I set the default for Usermin to "Always" for "Use HTML editor for composing?" option in the Writing Mail section of Mail Preferences. An error gets thrown and then things get weird. Trying to go back loops infinitely in the compose mail window, and the send doesn't work.
Going to the base :20000/ page manually also had the main area open to composing a message and any click loses the left-side navigation pane of the Authentic Theme.