You asked for it....
I don't think that's what the article is trying to say.
Figure 1 is simply detailing the internal waveform coming off a square wave inverter. It's totally above the centre axis of the graph, so there's no inversion going on there- that would have to be handled by a separate circuit down the line. And there's no way that is what they're blaring out of the back of the PSU because I'm not aware of -any- equipment, APFC or not- that would survive being hit by that kind of signal. Also, I'm not sure where you're getting 400V from because the graph is totally unlabelled.
I don't mean to question you here, but do you have any other evidence of this? I've discussed this matter at length with both Apple and APC over the span of approximately a month, and I was told exactly what that paper describes in Figure 2- that a stepped sine wave can introduce a "dead zone", and if that zone happens to be long enough an APFC power supply will simply shut off. Not once was I told or warned that a stepped sine wave could actually damage such equipment.
-SC