Merging contacts when creating mailing labels does not merge names correctly

in CRM/Contact/Form/Task/Label.php, the Merge contacts with same address option is provided. Logic is handled by the function "mergeSameAddress" The addresses are merged but only the first name ever appears on the merged label. This is because:

1. The first names and last names are not in the returnProperties, so are not fetched, so the names can't be merged using the logic in mergeSameAddress for matching first names and families
2. The addressee (and possibly addressee_display also needs to be set) value is never updated with the merged value in mergeSameAddress, so the default mailing label template will never apply