From zefram@fysh.org

Coercion from List to Set mostly works as expected, returning a Set
containing the objects that were elements of the List​:

(2,3,5).perl
(2, 3, 5)
(2,3,5).Set.perl
set(5,3,2)

but it loses when one of the elements is itself a List​:

(2,(3,5)).perl
(2, (3, 5))
(2,(3,5)).Set.perl
set(5,3,2)

I'd expect that coercion to yield a two-element Set in which one of the
elements is a List. Instead it's yielded a three-element Set in which
all of the elements are Ints.

-zefram

This was fixed in (2018-07-17) rakudo/rakudo@6ad096c

Tests needed.

Sorry, I left this comment thinking it's a different ticket. Nevermind, it's still an issue.