For that matter, Metallic has the same problem.
If you choose zero, you get no reflection. If you choose .001 for either metallic or specular, you get .5? I'm pretty sure it's .5, but it could be 1. I haven't tested that out.
I tried a few different newly created scenes, with imported geometry with a keyshot cube, and a keyshot ground (which oddly don't have UVs built in?)
CPU and GPU, no difference. Started in CPU mode as well, just to be sure there was no issue.
Oh, well....same/similar results in KS9.3 so maybe they just never really finished the generic material?