While I agree that is bad behavior, there is a case to be made against using dynamic pools for PD: https://www.ripe.net/publications/docs/ripe-690

I am aware of the 60sec lease time issue and reached out to mikrotik support about it. They said they’re working on fix for that in 7.7beta3 (I believe that’s the version they said from memory). They said they will not fix it in 6.x.

I am on 6.49.6 and passing Delegated-IPv6-Prefix through RADIUS to PPPoE and it's working fine.