iMessage text box does not clear after sending

Using Messages app on an iMac I find when I type and send a message quite often the message I sent or some portion of it reappears in the typing box hours or days later (like I never hit send). Even though the entire message appears above in the sucessfully sent area too. It also appears fine (as sent) on my iPad and iPhone.

I often see the spinning beach ball when sending the message too!