A very brief selection of FaxSTF as a printer did a number of automatic configuration changes without notifying me (BAD company! BAD! BAD!), including the placement of "Fax Server" into my Login Items. Once that was removed, I didn't have any further problems.
Thanks for your help, guys ... I'm feeling a bit sheepish, as I should have checked the Login Items first before doing anything. I just assumed that it was how I left it, and you know what they say about assuming.