As elginreigner has said the Address 'rules' will sometimes find 'broken' data with which the rules do not work. This is one of the reasons for the Address Block having an error flag option which can be implemented to make identification of problem records much easier. names and address data are often rather poor.
If you can predict, as in this case, that there will be a problem from time to time the easiest way to deal with it is assume that there will always be such a problem. Work out the rules you need to handle the problem and apply them to all records to ceate a suitable calculated field that can then be included in the fields used by the addrss block. Normally you only have to do that analysis work once and can re-use it many times if required. Sometimes you may come across a similar problem that presents a little differently but the chances are that a small adaptation to your original template work will deall with that too.