"Screwy E-M5 IBIS": Theory and evidence

I agree with Peter - you can't rule out #2 simply because the camera is on a solid floor - #2 refers to the sensor mechanism, which is independent of the camera body.

I don't have time to think about this at the moment, but probably I'd be looking at it in a different way - is the cause software, electronics, or mechanical. Unfortunately none of us really know the intimate detail of how the system functions, so really we're all just guessing wildly.