selected service reconfiguration bug
With the ability to reconfigure selected services in 3.1, there may be dependencies in once service on something configured in another.
One specific case is if you reconfigure postfix but not dovecot, you end up with virtual_transport = maildrop (when it should be vitual_transport = dovecot). If you reconfigure both postfix and dovecot, but nothing else, that is correct.
I don't know if there are any other similar cases, that's the one I found, but put a little thought to it as it's potentially a more general issue.