Now this is WEIRD:

At 10:02 this morning we lost access through the proxy. A quick peek
at the server showed that it had just refreshed the ACL and found 0
(zero) rules. I quickly jumped in to NWAdmin and, sure enough, the
*entire* rule list was gone. Empty. Elvis has left the building...

To my knowledge, no processes beyond normal net / file / print traffic
were occurring on the network at that time.

Before I begin an inquisition (and start burning people at the stake),
is there ANY reason for this to occur spontaneously?

Details: BM 3.8 on NW 6.5. Server in its own container, set as
master of that container (R/W's on 1 local and 1 remote server).
Sister server (in another city) is just fine.