If you delete a repo that has errata advisories attached to it, those advisories are still marked as attached to the now non-existent repo.

$ pulp-admin repo create --id="foo" --checksum=sha
$ pulp-admin repo add_errata --id=foo --errata=RHBA-2011:1771
$ curl -s -k --cert ~/.pulp/user-cert.pem https://pulp01/pulp/api/errata/RHBA-2011:1771/ | json_reformat | grep foo
    "foo"
$ pulp-admin repo delete --id=foo 
Repository [ foo ] being deleted
$ curl -s -k --cert ~/.pulp/user-cert.pem https://pulp01/pulp/api/errata/RHBA-2011:1771/ | json_reformat | grep foo
    "foo"

I would expect either:

a) repo deletion fails if one or more advisories are attached
b) advisories are removed from a repo when the repo is deleted