PRS

The opportunistic search trap kicks in if you try to search on a particular element of an object without having permission on all the elements in the object. To avoid the OST, grant permissions on all the elements of an object for a given qualifier, or specify the qualifier for which you have permissions in the search.

If you have permissions on address line 1, you're going to get caught with a wide open search on addresses. Similarly if you have permissions on all elements of address for "Business Contact" you're going to get caught unless you specify "BC" in your search.