Mike,
First,
I just wanted to mention that I actually like the fact that SCP is showing both the 1x and the LTE info together. Personally, I actually consider it a feature, instead of a bug.
Second,
While you and everyone else on this forum knows that I am not that knowledgeable about the technical aspect of mobile phone signal, I personally think the reason for duel 1x and LTE is that it might have something to do with Android Marshmallow forcing the Nexus 6 to stay connected to 1x and LTE, which seems to be the Fix for the problem that the Nexus 6 had with receiving calls while connected to WiFi.
Of course I could be wrong (and probability am), but that is just my thought.