I'm currently running version 24.4.0. I currently have the message pane showing and my Thunderbird settings such that a new message is marked read as soon as I select it. One thing I've noticed since this latest update is that sometimes when I select an unread message, its state gets changed to read and then reverts to unread.
I definitely didn't have this problem with previous versions of Thunderbird Portable.
I'm not sure if the problem is due to some change in this version of Thunderbird with regard to how/when the message status is updated between TBP and the IMAP server, if it's because my laptop is otherwise too busy, the speed of the USB 2.0 flash drive that I'm running from (a Mimobot drive), or some combination of everything.
Thoughts? Anyone else noticed a similar problem since this latest version of TB/TBP?