A job for running a nightly transaction log maintenance plan was created and owned by an account that was a member of the Domain Admins group. The account was subsequently removed from the Domain Admins group and the job failed (owner did not have server access), as expected.
The job owner was changed to another account that is a member of the Domain Admins group, and the job ran successfully for seven days. On the eighth day, another user, also a member of Domain Admins group, edited the maintenance plan to add a database. After the maintenance plan was saved, job ownership reverted to the original job creator (no longer a Domain Admin) and the job failed on its next scheduled run.