Hi Pilou, yes that's normal and intentional - the perp/perp snap will only engage if the initial pick point was within 65 pixels (actually 4 times the object snap radius) of the actual perp/perp location.

That helps to keep perp/perp to only engage when you pick somewhere in the general area of the perpendicular line, otherwise it was kind of weird when the base point would suddenly fly off to some far away location from your picks.

- Michael