dev-db/postgresql-base and dev-db/postgresql-server have a slot 9.0, while the postgres' virtual packages, that other ebuilds depend on, don't. please add the 9.0 slots to the virtual packages, too. Reproducible: Always Steps to Reproduce:
Since we don't need the virtual anymore and 9.0 is still masked there's no reason to add the virtual. Please wait until it has died an agonizing slow death :)