Counter-Intuitive Science

I think the reasoning is:
Since there is now a chance of Monty winning the car, your chance of winning the car (on the right hand side of your diagram) must be lower.I have given this more thought, and I am leaning towards the 50:50 answer.
i.e. You stand a 1:3 chance of winning if you stick, 1:3 chance of winning if you switch (and Monty has a 1:3 of winning).To use the normal teaching method for elucidating the standard Monty Hall question: Imagine that there were 100 doors...
You randomly choose a door (e.g. Door 15).
Monty randomly chooses 98 doors (e.g. Doors 1-14 and Doors 16-99).If you applied the reasoning of your image, then we would have a 99:100 chance of winning if we switch.
But that is incorrect: Monty has a 98:100 chance of winning.
Whether you switch or not, you would have a 1:100 chance of winning the car.If Monty was to actually open each of his doors (instead of just 'choosing' them), the the odds would only change if he choose a door with a car behind - i.e. you chance of winning is zero.

I think I was getting myself mixed up.If Monty randomly chooses a door (and doesn't open it) then switching is a 50:50 choice.
If Monty randomly opens a door with a goat, then you should switch.The chance of you winning the car has dropped (because Monty can now win it).
The chance that switching is favourable has stayed the same (if Monty doesn't open the 'car' door).Considering that I am posting this as I run out the door from work again: expect adjustments later!

I can already hear the crowd clapping and shouting "OPEN THE GOAT! OPEN THE GOAT! OPEN THE GOAT!" and the THWUCK! as Oprah cleaves open the goat with one swing of her mighty machete.
The crowd roars!! ...covering up the small, quiet sound of children crying.
No doubt the parents will reprimand them later for being 'soft'.But I digress...

The thing to remember is that we are only interested in answering the question: "Should I swap or stay?".If Monty chooses the car, then the question is moot; the answer is neither "swap" nor "stay".

I'll have a go at writing some code to do 1,000,000 iterations and I'll post the results.I should get the time and inclination to do it tomorrow.

I think the only disagreement we have is in regards to how the question is phrased and not on what the answer is.
1:3 chance of winning the car.
Stay/Swap is 50:50.

Imagine there were 3 people playing this game:You pick Door 1. Monty picks Door 2. I pick Door 3.We all have a 1:3 chance of winning the car.
But you are claiming that if Monty randomly shows a goat, then my chances of winning drop and yours increases, which is clearly not true.Remember, this is not the same as the standard Monty Hall question - Monty doesn't know where the car is.