Possibly a bug with sort order with discnumber 1/2, 2/2

I have had a lot of trouble with a bunch of mp3 files ripped from two cd’s where the ‘Discnumber’ is either the strings ‘1/2’ or ‘2/2’. In the end I divided the files into two folders and labelled cd1 and cd2 and I can now play them in the right order. I am slightly suspicious that php may be evaluating these strings to 0.5 and 1. There may also be something else wrong with my tags that I have not worked out. I could not determine from changing tags, file names, or order written to the disk, exactly how Volumio works out the display order.