Compose window stay open

Hi guys,

I am using PTB on a usb flash drive. When I compose mails and hit the send button, it sends the email but the compose window stays open. The mail appears in the Send folder, but the compose window icon keeps showing in the task bar. When you click on the Compose window icon in the task bar the compose window don't pop up, but if you open up the "Task manager" it says that the compose window is still running as well as Thunderbird. So if I select the "TB compose" window process it just closes TB all together.
Any idea why this happens.
I see there was a post last year where they had the same problem (see post on https://portableapps.com/node/3881) but the post stayed unresolved.