I just noticed that this property exists only when it its not a default value. If the node's position is (0,0), the position property will not 'exist', getpropertylist() will not return it, "'position' in object" will return false and if you try to access it, it will yield an 'invalid get index' error. This also happens with scale, and probably other properties too. probably this is the way an instance placeholder works. It will store whatever non default property you set in the inspector and create dynamic properties for it.