Here is an online virus scan report of the file http://greedygammon.com/greedygammon.exe
(click the image for full size)
You can check it yourself and see it is clean.
No one else reports this cube issue, so I doubt it is a bug from the program. More likely a problem from the user side.
Also i can't compile the full installer version because the digital sign certificate has expired.
It costs $140 for 2 yrs and I can no longer afford to buy it. Some years I don't use it at all if there is no update.
So anyway maybe in future GreegyGammon will move away from old MS Windows download version of a game which is getting old fashion by now.
Many games now run from within the browser, no download required and the app will update itself.
msolomon GreedyGammon support