It's been blissfully simple:Let me know what the results of the UPCP run are.
Ftp Quota Check v1.6
Mara-1, FTPQuota-0 (if we're only counting *this* round).
Thank you very much for your help! My only theory on why it was picking those user accounts (and only those) is that perhaps something was left over from an upgrade. Or cPanel gremlins.