Ummm... sorry if I'm being a little dense... but what is the problem? You had your emails sorted in descending order and then when you clicked on the date you reversed the sorting. It should be fine now. Is the issue that it's reverting to the wrong order on its own?

I am sorry you could not see the pictures I uploaded. After installing the new version of tbird, my newest messages coming in appeared with the oldest messages (2008). The only way I could get them into the right part of the queue with the newest messages was to toggle the date column twice. Interestingly, they appear in the right place today without a restart, just lots of sleep overnight.

I did see the images. It seemed like a sorting issue that should be easily resolved in exactly the way you did it. You probably simply clicked on one of the headers by accident. I do it all the time, especially when I'm trying to click on the top message. It's like the pointer is actually clicking 5-10px above where I want it to. In any case, as long as it's easily rectified and doesn't keep happening on its own, I don't see an issue and you should mark it as solved. Or am I missing something?

I can think of no reason why a message from 2015 should automatically appear in the inbox (in date-descending order) with messages from 2008.

Possible that there was simply a 'hiccup' in the rendering of the code. It simply dumped the new email anywhere (no rhyme or reason) and when it refreshed itself (when you resorted and/or restarted) the code began rendering properly again. Programs do self-correct. It's one of the reasons why restarting programs and/or computers often works in resolving some issues. An automatic update may have triggered it or a background process. As long as it doesn't continue or cause havoc with something else, I believe you're fine. If it does, re-post, and provide as much detail about what was happening before and/or during. Fair?