General :: Sort Generates Unexpected Results

I sorted a large mailing list and the result is in almost sorted order, but not quite.The sort was invoked in the default manner, just "sort".See (below) a segment of the output file.(Note: the actual files have a street address following each name.I have omitted the addresses to avoid complaints about disclosing personal information on-line.) I expect all people named KATZ to be grouped together, but they aren't. This phenomenon occurs elsewhere in the output file, so it has nothing to do with surnames beginning with the character string KATZ.