Multiple PostgreSQL running as primary server on pgpool
Old post, but as I have just been through the pain of configuring pgpool, and have encountered similar problems, I'll answer here.

I have exactly the same setup, but I made the choice to go through this excellent tutorial (in 6 parts ouch). It intends to build a full pgpool/pgsql HA infrastructure, where there is no single point failure with one pgpool server, as two pgpool are installed along two postgresql primary and standby servers in streaming replication.

Anyway it is quite easy to adapt in order to keep pgpool one one separate server like I did.

Regarding our problem here, I think it could be related to an incomplete primary/standby setup. And anyone having this problem shall try to setup streaming replication at postgresql level before trying to attach new node with pgpool (particularly when you have a database that is not empty).

In postgresql.conf I would check REPLICATION section on both servers and make sure that the standby server has hot_standby = on. Make sure also that you have correct recovery.conf file on standby server.