1. I believe the EV slider is meant to be disabled if you're manually setting the shutter speed and ISO.
2. Yes, I agree with you that when I go to P mode from M mode (after having set both shutter speed and ISO manually), the EV slider still stays disabled. I believe it should not. It should be enabled.
3. Question for the dev: When I launch ProShot app, it usually opens in M mode, because that is what I use most often. Also, the ISO at start-up is usually 100 because that is what I use most often. The shutter speed is whatever it was when I used the app previously I guess. Under these conditions, the EV slider is enabled, and I can slide it to the left or right, causing changes in brightness in the viewfinder. This should not be the case, no? (However, the photos come out the same with any EV setting, which is expected because the shutter speed and ISO are fixed). Also, when I change the ISO to, say, 200 the EV slider gets disabled, and is enabled only when ISO is set to Auto. This, I believe, is expected behavior. So my question is: when I launch the app in M mode with a non-auto ISO value, why isn't the EV slider disabled right away?