I need to correct the above description.  It only happens on replies and forwards, not on compose new.

I just recently installed this extension and I am immediately having the same problem. The MxHero sends the email, but it never appears to be sent, never closes the compose window and stays in drafts until I delete it.  This happens on both reply and compose new.  It also happens on both my personal gmail account and my google apps for business account.

Thanks for any help.