Covering prefix blackholing traffic to one of its covered prefixes....

We have dual-homed sites that only accept routes from their peers, and default to their transit provider. A site may receive a covering prefix from a peer, but since they are not accepting the full table from their transit provider they don’t see the covered (i.e., more specific). In some cases the peer announcing the covering prefix blackholes traffic to the covered prefix. Is this accepted behavior, or should a peer announcing a covering prefix always delver packets to its covered routes? Does this happen often? Thanks! Steven Wallace Indiana University