First of all please restart application and try to reproduce this behavior. It can be some post-install mess.
If issue still there, then I would like to see your log files (Instructions for collecting Alert Central Logs)
Also what mail client you use for response? Do you include some additional attachments or signatures in letters?
There is Beta of new version coming very soon (this week, I expect). So upgrade maybe one of solutions (IMO it worth to try).
It was as simple as restarting the app. Appreciate the help.