If you can consistently get it to flip back and forth like that, it would be interesting to know how the fuel trims differ. A realtime OBD data stream reader would show those values, along with possibly other things that might help explain what's going on.
At this point I’m just thankful to have found something that works. I’ll experiment periodically, but will most likely just stick with ethanol free as long as the results stay the same. It really is a great vehicle! Hopefully others will try to duplicate my findings, and compare notes.