The one you're talking about is different. What you reported isn't a bug. I looked into it, and it's not terribly efficient for me to handle it otherwise currently.
The line across the top where your current inbox count is displayed gets calculated and displayed *before* whatever message is going to show up, whether that message is that your message was sent successfully or there was a problem sending it.
It seems a minor enough issue that I don't think it warrants (currently) a major rewrite of the process that takes place when you submit a message. That rewrite would basically be determining whether or not an error occurred before taking you to the screen that says whether or not an error occurred. It's something I can get to, but I think it's appropriately pretty far down the list.
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