Lately, I see (too) many messages appear twice (or even more). IMO, this wasn't before.
Now, I think you (Michel) created some test for that, because just a minute ago I saw the message "You created the message already" (similar). However, I did not at all, BUT I did a preview.

So, the preview just appeared, I crossed it away, and pressed SEND. Then the message appeared immediately (as if you check for this in Java). And ... the message was already there indeed ... Am I seeing things ?
JFYI.

Peter