In my production environment (5.0.9 OSS), users can't sort messages by sender. We don't know exactly when this feature stopped working, but in older versions we had the normal behavior: disable sorting by sender when in "by conversation" mode.
Any idea how to solve this?
I have search bugzilla for this bug, but no one seams to have ever mention this. If another person here faces the same problem, please raise your hand so I can ensure that it is really a bug and I add an entry there.