Final update. I contacted Amazon 'chat' support and the person I spoke to asked me if my Collections were in alphabetical order. When I said no they told me that I should reset to factory settings and the collections would then be in alphabetical order and all would be OK then. Don't know why that was going to help my situation but I was pretty much OVER it by then and willing to try anything. Never mind that it had taken me weeks to get the kindle to the point it was at then - I have many files on my kindle which I had to convert before I added them.
Needless to say there was no alphabetical order to my collections and I had to go through the whole process with my files once again. All seems OK now. Thanks for your help.