Catalog zones ignores already loaded non primary zones on secondary

Sequence of events:

1. A forward zone foo.com not loaded in named as part of named.conf on Primary;
2. A forward zone foo.com already loaded in named as part of named.conf on Secondary only.
3. A Primary zone foo.com is added to Catalog Zones as primary zone on Primary server -- Success
4. Catalog zone transfer took place
5. Secondary servers added zone foo.com as Primary zone though Forward zone foo.com is already loaded.

According to the draft RFC for DNS Catalog Zones https://tools.ietf.org/html/draft-ietf-dnsop-dns-catalog-zones-01:

" If there is a clash between an existing member zone's name and an incoming member zone's name (via transfer or update), the new instance of the zone MUST be ignored and an error SHOULD be logged." (6.1)

It appears that the catalog zone code is probably checking the zone table for an existing zone called foo.com, but it's not checking the forwarder table.