Mechanical shaft connection arrows should be bidirectional

From what I can tell from the tooltip on the turbine, a mechanical shaft can transmit power both ways - anything connected to it contributes to the shaft's inertia. However, shaft-connected machines show an input and output arrow for the shaft, which would seem to imply that power is only transmitted one way along the shaft (as if each machine had an overrun clutch).

I don't think there should be arrows at all on something that does not provide force along the axis of a rotating shaft.