Can’t Keep Update Filters Checkbox Checked

Tiger server 10.4.9. In Server Admin/Mail/Settings/Filters, I can put a checkmark next to “Update the Junk Mail and virus database” entry, and then specify number of times per day to update (e.g., 4)… but when I click the “Save” button, the checkbox UNchecks itself after the Save is completed. Last Update says “Not available” even tho I see in the Virus Database Updates log that freshclam does daily definition updates okay.