Issue : It seems that stacking the "Upgrade garrison elites retinue to palace guard" and "Imperial Guard Garrison Retinue" will swap the defensive retinues to the Eight Prince defensive retinue.
(Look at the Garrison provided)
(The garrison retinue in question)
Reproduction Step (from turn 1) :
- Be the Emperor (Hence gaining the Imperial Garrison in your capital)
- Build the Palace in your capital
Reproduction Step (from the save since it was a modded game) :
- Press the upgrade button to upgrade the Palace to Tier 5. This will turn the garrison into the double stack garrison (the weaker garrison)
- Demolish the Palace back to tier 4. This will turn the garrison back into Protectors of Heaven.