I have noticed a very disturbing bug in the latest version of Virtualmin. I am running the following:
Virtualmin Professional 3.19
Upon making a simple, unrelated modification to one of the accounts in a customer domain, many of the e-mail addresses in that domain were disabled. In particular, the change was only to increase one users quota with Virtualmin, which appeared to work successfully. However, I noticed afterwards that many lines were missing from /etc/postfix/virtual, which was modified at the exact same time as this quota change. In fact, the Webmin Actions Log shows exactly what happened, including multiple unrelated changes to /etc/postfix/virtual, paired with multiple executions of the postmap command, all before executing the simple edquota command that was requested.
I will submit additional details if I can find a pattern to shed light on what happened. Please note that this does seem to reproduceable.