by Tony Neath.
I did A bit more testing.
As the 2 courses I am backing up are only a few Megabytes I was able to run the command line backup on the Windows server.
This produces the same result with backup_auto_keep set to 5 the oldest backup of the 4 listed is deleted and replaced with a new one.
I then edited the database with PhpMyadmin so that the backup_auto_keep value was 3 and this kept 2 copies of the backup.
I have requested some help from a php developer at my college next week.