I've made about 6-7 of these kits. My favorite Coopers kit!
The way I make it is I use 1.5 lb malt extract, 1 cup corn sugar, brew for 2 weeks at about 15C/58F, transfer to secondary for 1 week at room temp, around 20C/68F. Then I bottle/keg.
I've never had any bad off-flavors, but this...