Let me say that I'm not the expert. I'm a little new to WGT, and I've only played 9 holes of real golf in my life.
I don't know why I've seen this happen as well. But I can postulate a lot of things, and try and understand.
The physics of the game and real life golf may be different.
Inasmuch, in the case where the green cants from back to front, perhaps a ball w/ a lot of top spin will lose traction (in the 'computer's mind') and slip down according to the programming of the greens physics. Seems a little strange, though.
[Maybe something like a car on an icy road going uphill can 'top spin' its wheels forward but this causes something like hydroplaning and the car will slip downward.]
Can any player address or answer this questions ?
#1 Does this happen on a flat green, too? I have to test it, myself.
#2 Will a little less top spin solve the issue? #2a Does it?
#3 During what cases and conditions of the game do these issues not arise (with a ball with full BS) , and how do they differ from when they do happen?
#4 What happens when the opposite is applied?: A ball w/ BS on a green which cants front to back (the reverse as above).
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WYLBILL I may not be helping much, but I have had the same questions, because I've seen it happen to me.
JF
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I like the word 'postulate'- suggest or assume the existence, fact, or truth of (something) as a basis for reasoning, discussion, or belief.