Comment 6 for bug 173051

> The mechanism you are suggesting is identical to an old one I had which
> I rejected for the OnReturn one. I still think it is less
> straightforward than the OnReturn one.

Well, you can combine both:
if user leaves subject field: check if he hit Return
  if yes: do nothing
  if no: remember this
if user sends message: check if we remember that the user changed/set
the subject?
  if no: do nothing + send message
  if yes: send subject update + send message

--
Mvg, Sander Devrieze.