Both the demo script (from the top post) and the one-line test case (2nd post) now pass without error!
Bisectable identifies a commit from last week as the fix:
https://gist.github.com/97d96022fdfed416e67ecadf5b2b9353
https://github.com/rakudo/rakudo/commit/231cb3f
Is there a way to write a spectest for a probabilistic bug like this?
