pschmoker,
I also bought my rx400h used. I had terrible mileage for the first few months until I perfected coasting and more importantly, until I replaced the auxiliary battery. The original has a "magic eye" thingy on it that indicates battery damage. Mine was nice and blue so I thought it is fine, but then the car had to be jumpstarted (yes, it was very embarrassing) so I checked the battery and found that 2 cells were shorted. The "magic eye" was in a third cell and that very cell was ok, so it showed blue.
I do not know what the connection is, lemon, the op here is much more knowledable than me, but I suspect that some sensor running off the aux battery reports false data and that misleads the controller to fire up the combustion engine...
My advice would be to replace the aux battery if you can borrow one, do the learning procedure and see what happens.
Let us know!