Was the "order" that you saw related to timestamp of the LISTSERV or the order in which they were enqueued in you inbox?
Assuming PANIX is your mail domain, I see three different IP addresses associated with DNS MX records:
> set type=mx
> PANIX.COM
Non-authoritative answer:
PANIX.COM MX preference = 150, mail exchanger = mx.PANIX.COM
mx.PANIX.COM internet address = 166.84.1.72
mx.PANIX.COM internet address = 166.84.1.73
mx.PANIX.COM internet address = 166.84.1.74
So, depending upon availability and load, is it possible that different hosts were involved and all that that implies?
/pete