A7S Auto Exposure Lock not working with Shutter Priority?

So I've been fiddling around with my A7S, as we all are, and if I shoot Shutter Priority, ie setting the shutter to 1/50 and letting the camera choose aperture, the AEL toggle stops working. It works in all other modes. The main use for that button is to make the camera NOT do any further adjustments, yes? Well, my camera flutters the aperture like it's motor boating.

The button successfully locks down ISO (if auto), shutter speed (if in Aperture Priority), etc., but not the aperture while in Shutter Priority mode. This is all in Movie Mode.

Are you guys having problems as well? As a side note I have NO native E-mount lenses, just EF and M43 via Metabones.
 
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