Can't bind to a Pair with a subsignature

[masak]

<masak> r: for foo => 1, bar => 2 -> (:key($k), :value($)) { say $k }
<p6eval> rakudo cecc9f: OUTPUT«foo␤bar␤»
<masak> n: for foo => 1, bar => 2 -> (:key($k), :value($)) { say $k }
<p6eval> niecza v22-33-gda13155: OUTPUT«Any()␤Any()␤»
<masak> sorear: awww :)
* masak submits nieczaissue