@maiyannah As written in the above mentioned discussion, I think this behaviour of the server would be much better, even better than Twitter does ;-):
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Meanwhile I checked how Twitter responses to posting the message ("tweet") with duplicated text. It returns HTTP error "Forbidden", even if the duplicated message is not the last message sent by this user.
It will be far more intelligent to respond not with an error but as a successful sending of that previous message. 
Thus a client application (and a User of that application! ) will know that the message it's trying to resend was actually sent earlier. And stop resending!
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See https://github.com/andstatus/andstatus/issues/83
What do you think?
@gargron