If you are saying the body has to be set at 1/8, this should work, as this speed consistently locks accurately. Again, manually changing speeds to 1/15, 1/30 and 1/60 messes things up, because the speed dial is locking the mechanism in between speeds at these settings. If the leaf shutter lens 'takes over' from the speed dial I believe there's a good chance the 90mm would kick the body into action? Hope you understand me.
Something else I should add is when in dry fire mode, pressing the shutter rapidly and cycling between speeds, all the speeds work fine and the shutter never sticks, as if I'm quickly shovelling coal into the furnace - the engine chugs along. When film is loaded, and naturally, changing speeds and pressing the shutter is more random with long intervals (looking for pictures), the camera becomes dumb. Such an odd piece of equipment. But anyway, from this idiosyncracy I know the speeds themselves are accurate.