Eagon's Map device bugged? limited scarab slots

Is Eagon's map device only supposed to have 3 slots for scarabs? I've unlocked my other 2 map slots so that's not the issue I'm just wondering if this is intended? If so then the memory tears are just really bad because you are -2 scarab slots, doesn't make much sense to run them. I also swear that I've put extra scarabs into Eagon's device that either are in an invisible slot or just ended up poofing out of existence.