When trasnferring Pumpkaboo between instances of PKHex, or when "evolving" a pumpkaboo (ie., setting its species to Gourgeist), its form is always set to "Average Size" regardless of the pkm's actual size.
Noticed this in the May update of PKHex, occurred when dragging Pumpkaboo from an X save to a Y save. Also noticed this when setting species from Pumpkaboo to Gourgeist on the X save (without moving it to the Y save.)
This affected all sizes: Small, Large, and Super. 4 affected pokemon were caught in-game, 2 affected pokemon were from the "Boo! A Pumpkaboo!" wonder cards.
Have not tested with ORAS save files yet.