If I, e.g. :sort date and then open a message, upon returning the sort has been returned to the default (:sort -r date I think).
I do see the same issue although most of the time I get around it by running my
:sortcommand and then going through the sorted messages in the message view (without going back to the main view). In this case the sorting seems to be preserved, although going back to the main view does not preserve it. I'm even tempted to think that it might be deliberate.
Gah... no, even in the message view when going through all messages, the sort order is lost :\