ICE runs unnecessarily

2006 I-Tech Prius, 17,000 km, a/c and radio turned off.
My Prius has developed a new symptom which I first noticed about a week ago.
On a day when the air temp was about 20ºC I drove about 100 km and then went down a long hill that produced all green bars on the MFD. Drove up a small hill and arrived at a turn-off showing one less green bar. Drove along a flat road for about 100 yards at about 30 km/hr and lifted my foot of the accelerator to slow down. Green arrows appeared on the MFD and at the same time the fuel consumption showed 2.4 L/100km.
Next day the same trip gave the same results. I went round the block (no long down hill run) - same result.
Today in a different location I noticed that I had all green bars so I took my foot of the gas and the MFD showed a fuel consumption of about 2 L/100km. This time I selected EV mode and the consumption dropped to zero. Turned off the EV mode and the fuel consumption immediately rose to 2 L/100km. The engine would have been hot and I had all auxiliaries that could be turned off, turned off.
Before I take my car to Toyota for testing, I thought I would ask if anyone could explain this symptom. Note: It is summer here so severe cold does not apply.

 

I would have thought the engine was warm enough. I have travelled the same route in much colder conditions without problems.
However, I will try the stopping for 6 secs to see if that makes a difference.

 

The aux battery is holding a good charge so I doubt that this is the cause. However, you never know so I will take more note of the battery condition.

 

I drove out of my yard this morning (temp 19ºC) and noted that the MFD showed all green bars. After 200 yards I took my foot off the accelerator and the fuel consumption dropped to zero. I did this 3 times all with the same results.
After 200 yards I would have thought the ICE would still be cold yet it turned off. I travelled about 1 km and by that time the green bars had turned to blue. Out of curiosity I lifted my foot and the ICE once again turned off.
I was surprised that the ICE turned off before the it warmed up. Is this normal?
Where can I read about stage 3a and 4 driving?
I am beginning to wonder if this odd condition is the cause of different fuel consumption figures over an ofen travelled route. Previously I thought it was affected by the wind or load in the car.

 

Thanks, jhall.
Having now read Bill Merchant's article on the 5 stages of operation I am more confused than ever.
Going back to my initial post, I did stop at a stoplight for at least 10 seconds (more like 30-40 secs) before climbing the hill and turning into the place where I first noticed the ICE running when my foot was off the accelerator. According to the article, I should have been in stage 4 but it seems I was not.
In my last post, I should have been in stage 1 because the ICE had not warmed up but it seems I was not because the ICE shut down when I lifted my foot off the accelerator. I doubt that I was in stage 2 after only 200 yards.