On closer inspection, I just realized that this is a bug! The grass' drawing code uses || instead of && when doing the collision check, so essentially the player's status will always count as "in my particular patch of grass" and trigger the additional head drawing. Changing the the collision check ||s to && in obj_tallgrass_32's draw event (lines 13-16) should fix this. (obj_tallgrass_64 inherits everything from _32 so you shouldn't need to change that)