Hmm, I just had this crop up for me. Rendered the same scene three times in a row with very slightly different materials on some objects (trying to solve something else). The first two times, I had very soft shadows. The third time, I had crisp and sharp shadows. I hadn't made any changes to the light, I didn't even select it at any point. All three times using 12.0.306, superfly render.

So it's not just that superfly is ignoring this setting, it's that it honors the setting inconsistently. That's even worse, since you can't predict what the outcome will be.