I had the message window freeze up after hitting send once or twice, no errors or anything. I just waited a minute or so and restarted the client and the message had been sent so I don't think it could cause major problems with trades. It might just have been me though, so I'd call it complete. 
It's nothing. I wasn't very careful when writing some of the event code, and the event thread is blocked after most of the button presses. It's easy to fix, but it does look like Dark Exchange is locked up. All you have to do is wait a few more seconds (possibly minutes) and it should work itself out.
I added an issue for it.