The "recipients of mailings not completed/sent" issue is a bug (mailing filter wasn't working properly). Fixed in r11668.
The "can't type in text" behavior reported is probably due to the fact that the mouse cursor must be clicked in a "populated" area of the editor box (initially the upper left hand corner). We expect this behavior (as well as the non-ideal HTML/WYSIWYG mode switching behaviors) to be improved with Dojo 0.9 - which we plan on incorporating in 2.0. I've added help text to the screen as a "partial fix".
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Weirdness from the WYSIWIG editor in the mail sending wizard, i.e., can't type in it, text disappears when switching between regular and HTML-view modes.
Related Suggestion: Admin Option to disable your WYSIWYG widget so that TinyMCE or something else can be used instead, if desired.
Also, an entry appeard in the message recipients selectors for a message for which I never completed the wizard. I don't think this occured in previous versions.