[perl #63686] Can't iterate over junctions in hash keys

[via RT]

# New Ticket Created by  Moritz Lenz 
# Please include the string:  [perl #63686]
# in the subject line of all future correspondence about this issue. 
# <URL: http://rt.perl.org/rt3/Ticket/Display.html?id=63686 >


This works:

17:58 <@moritz_> rakudo: my %h = ( a => any(3, 4) ); say %h<a>.WHAT;
17:58 < p6eval> rakudo f6cdf9: OUTPUT«Junction␤»

This doesn't:
17:55 <@moritz_> rakudo: my %h = ( a => any(3, 4) ); for %h.kv -> $k, $v
{ say  "$k: {$v.WHAT}" };
17:55 < p6eval> rakudo f6cdf9: OUTPUT«a: Int␤a: Int␤No exception handler
and no message␤current instr.: 'return' pc 16018
                (src/builtins/control.pir:39)␤»

(I think it's correct that it autothreads over $k because it's not
declared as Object, but it shouldn't throw an exception anywhere).

Cheers,
Moritz