At last, thank you Peter, I finally managed to find out why my books were not in authors' alphabetical order. I had used Author Sort in Calibre's Plugboard & of course needed just Author - simple when you realise why!!
Suggestions for new solftware update - I agree the authors or library list in some form of alphabetical grouping would be good. The slide bar is too vague & if you have lots of books in your library it can be pot luck to find the author's surname without trawling through pages. The shortlist helps but if you read a lot of books, you arent always sure which you are going to read next.