Sorry, no, it's a bug; pbuilder has enough information to select the right keyring or revert to the old behavior when one selects to create a Debian environment from an Ubuntu host or vice-versa.
This should be solved by pbuilder selecting the keyring based on the target release rather than having a hardcoded default keyring which gets used for all pbuilder create runs.
Sorry, no, it's a bug; pbuilder has enough information to select the right keyring or revert to the old behavior when one selects to create a Debian environment from an Ubuntu host or vice-versa.
This should be solved by pbuilder selecting the keyring based on the target release rather than having a hardcoded default keyring which gets used for all pbuilder create runs.