That's a houserule yes, but it makes the staff even more overpowered. I know that a staff especially an iron shod quarterstaff is a very deadly weapon, and it has reach and it is very fast, can be used in all kinds of moves like tripping vaulting etc. But still that requires the use of both hands, yes you can let go to extend your reach using only one hand for a short time, but I see no way of efficiently fighting with a staff and a shield. So that should not cause the same range like a shortsword eg