I'm glad you mentioned the low-energy after wash rinse. Mine behaved totally different than it usually does the other night; it was a load of not horribly dirty dishes since most was just veggie juice residue and such, but a few plates had spaghetti sauce plastered on. Used Normal as usual with no options, but instead of the usual 2-3 prewashes with purges between, it opened the detergent cup a few minutes in, no drains at all. What struck me odd about it was that I've had less-soiled loads than that - that ended up getting prewashes, which I thought was unnecessary. I was pleased really, because I always loved that the PowerCleans jump straight into the wash on Normal, so the detergent gets a full workout. I'm not sure why it decided only now to do a low water cycle.
Anyway, the first rinse was like you described, it wasn't a purge, because it filled with more water than the normal 5 seconds or so, but it also wasn't a full water charge. The pump would kick on for 20-30 seconds, and had a few seconds of good spray before hearing the pump start cavitating, but it seemed like it was on purpose. It would run for that little period and then sit for 30 seconds, and repeat. It's the first time I've ever noticed it do that. Almost like it was intended as a filter purge that also had a little wash action thrown in.
After that, it filled and finished out normally with the long final rinse. The cycle was a PowerClean Normal cycle exactly; Main Wash - Purge - Final Rinse. I can't imagine it used any more than 3 gallons, if that, but as always everything came out squeaky clean with not a speck in the filter. I'm wondering if that super baked on heavy mega test load forced the sensor to recalibrate, and after that carnage, it decided this load was a walk in the park, haha.