Why do I get surname only results for lives entirely outwith my search limits?

If I specify a known named person for whom I need information by forename and surname, place and beginning and end of a search period, why do I get answers by surname-only for dates and places unrelated by centuries and enormously large degrees of latitude from anything I have asked for? I've just been offered surnames for US Civil war recruits as candidates for a Jamaican parish minister of the 1780s.