Not sure if this is based on 5e rules but the issue is with the prepared spell slots. I have a regular Wizard and Gale in my party. When I equip the headband my Prepared spells number increases from 5 to 7. When I switch the equipment to Gale the number of prepared Spell Slots is reduced but the number of Prepared spells stay the same. allowing me to have 7 out of 5 as prepared. This does not reset on a short or Long Rest. Basically by passing the Headband around all Mage Characters can have 7 prepared spells at all times.
