Purchased my first honda. A new 2009 trx 420FG "Canadian Trail Edition" that is equiped with the automatic shift option. (Not the left hand button shift, but a fully automatic shift where the machine shifts for you)

My question is regarding the operation when decending a long hill. When I start down the hill in first gear and then use the rear brake to slow my decent, the quad reacts to the application of the brake by trying to downshift further to a non existant gear causing a transmission chattering situation. Is this normal or is something amiss?