[Dovecot] starting multiples instances of dovecot listening on same port

[mymailingslists at gmx.at]

Of course it's useless and this just can't work ... if I try it returns with
an error message.
Can't bind to port xy.
No problem, that's the way it should be, but further strange things worth
mentioning happen. After the second instance quits with error msg, the
currently running instance doesn't accept any client connections anymore.
Needs to be restarted.
(currently I'm only using dc 0.99.10.9 as pop3 server)

That's really no problem, but strange :>
(I admit I'm somewhat curious if this problem is specific to my setup or if
its happening everywhere)