a combination of key clicks causes rogue tabs that can't be closed

Get blank tabs that won't close. Here is how to re-create it...
open Postbox like usual, right-click trash and empty trash, compact trash, then right-click and compact inbox. While compacting (sometimes the status bar states 'done'), click on the attachment, link or photos button in the tab bar area. I get a tab that shows with no title and I'm unable to click and close. I end up restarting postbox to get it to clear.