I don’t know about the deep South today, but many of the Black people that I know and work with address me and others this way, ‘Miss (First Name)’. I do hear it more in reference to females than to males.
It threw me when I first encountered it but I’m used to it now and often use it myself.
As I stated earlier, it is a subservient thing, akin to touching the brim of a cap/tugging at a forelock of hair ( which is for males ONLY to do and a long dead thing of the past in the UK )when seeing one's "betters" ( always re a tenant farmer on an aristo's palatial estate/"pile" as they say in the UK) pass by.
It has less to do with "manners" than it has to do with "knowing one's place"! And descends, vis-a-vis blacks, from slaves saying:"MASSA JOHN" etc.!
And then there are the various different ways/terms that the natives of parts of the old BRITISH EMPIRE used to use when talking to or about their employers/people of distinction: sahib, in India; which is the most well known one, for example. And that was still a subservient term!
Absolutely NONE of these things have ever had to do with "manners"; a term, which sadly, few understand or actually use anymore!Manners and politeness are something quite different.