Right side Fn + Shift + PgUp don't work together

If I hold down Fn + Shift + PgUp (all on the right side), it doesn’t respond. RShift + PgUp works, as well as RFn + PgUp (and RFn + RShift + PgDn). Has anyone else seen this? Is this a hardware or software limitation?

It sure would be nice for lazy one handed scrolling through long terminals…