Here's a C program that simulates exactly how rakudo creates nums from strings and shows the same problem:
https://gist.github.com/zoffixznet/46ae8dd7d85096d58dc557f60f82a179 Here's an IRC conversation with the author of the post you linked to followed by investigation and discovery of this problem: https://irclog.perlgeek.de/perl6/2017-07-13#i_14864050
