Superseding jobs not working as expected

I created a job with the following schedule:

- daily full backup @ 1pm every week day
- weekly full backup @ 1pm every Friday
- monthly full backup @ 1 pm every last workday of the month

Whenever the last working day is a Friday the schedule operates as expected: the monthly backup runs. The weekly & daily backups are superseded.
However when the last working day is not a Friday the scheduler tries to run both the daily and the monthly backup. I expect it to run the monthly backup and supersede the daily backup.
Am I missing something here?