Greylisting bug, Postfix get a connection refused to 127.0.0.1:10023

Server details: Ubuntu 12.04.5, Virtualmin 4.13.gpl, Postfix 2.9.6, Postgrey 1.34

When I enable Greylisting through Virtualmin the server stops to receive email because Postfix can’t connect to Postgrey service. At /var/log/mail.log:

warning: connect to 127.0.0.1:10023: Connection refused
warning: problem talking to server 127.0.0.1:10023: Connection refused

But Postgrey service is apparently ok, with this result of lsof -i:10023:

COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
/usr/sbin 14843 postgrey 5u IPv6 2760692567 0t0 TCP localhost:10023 (LISTEN)

It seems that Postgrey is using IPv6 loopback address and I suspect that running it with postgrey --inet=127.0.0.1:10023 would solve the problem, but probably with a restart it will run again in IPv6

How to properly change Virtualmin configuration to avoid this?