How do I stop my IMAP and SMTP settings from automatically changing to wrong numbers every few days?

Internet provider is Comcast. I know the correct IMAP and SMTP port and SSL settings, but every day or so, I stop getting emails (either that I send to myself as a test or that I know someone has sent to me) because the correct port setting keep reverting to wrong port numbers. So I have to go to Account Settings, click Actions, choose Add Mail Account, enter my current email address and password, and wait for a message that tells me this account already exists. At this point, if I go to Manual Configuration, choose AutoDetect for both IMAP and SMTP SSLs, and click Re-test, the correct port numbers return. I click Done, and then I can receive incoming emails again -- sometimes for a couple of days, sometimes for only a few minutes, before the wrong port settings reinstall themselves and I have to go through the avoid steps again.