I never thought I'd get so into a conversation about a beer style that, after a flirtation in Bavaria in summer '85, I probably feel like drinking once every couple of years. Beer + science = addictive fun.
Simple: maltase breaks maltose into glucose, but it is denatured at a low temp and so is not active in a normal mash. Adding the partially converted and fully gelatinized material to the cold portion that still has Maltase allows it to have a go for once. In the normal mash Glucose has nothing to do with the lower temp rests, it's just part of the normal product of amylase activity.