Yes, there is a shift-left when those are enabled. I use Dominos so I never see the right-side bars and
I could have sworn they were all disabled. Are the on by default now and I missed that? Anyway, that's the hidden _X modifier variance.
I knew about that but because I'm getting both X
and Y shifts, I (foolishly) discounted it as a possible cause, and it turns out it is only affecting the _X, not the _Y, which retains its strange deviations.
Instead of _Y=70, I'm getting 85 or 94. I've been through the interface settings and they're the same across the chars I checked (and all special action-button bars disabled). I could accept that 70 is the base and something or other gets tacked onto that, the question is what?