This works now as expected: <bartolin> m: sub Foo(uint32 :$bar) { say $bar }; Foo(:bar(4)) <camelia> rakudo-moar ae6177ca2: OUTPUT: «4»
I think, it was fixed with https://github.com/perl6/nqp/commit/fc727ea911 (bisectable pointed to the corresponding NQP bump). Since the tests in S02-types/native.t are passing, I'm closing this ticket as 'resolved'.