From @jnthn

01​:21 <@​jnthn> rakudo​: my %h = B => 2; my $x = "ABC"; $x .=
subst(/(<[BD]>)/,
{%h{$0}},​:global); say $x;
01​:21 < p6eval> rakudo 695300​: OUTPUT«A2C␤»
01​:21 <@​jnthn> rakudo​: my %h = B => 2; my $x = "ABC"; $x.=subst(/(<[BD]>)/,
{%h{$0}},​:global); say $x;
01​:21 < p6eval> rakudo 695300​: OUTPUT«Use of uninitialized value␤Use of
uninitialized value␤AC␤»
01​:21 <@​jnthn> Nailed it.
01​:21 < DanielC> spaces?
01​:22 <@​jnthn> DanielC​: Bit more to it than that. Those two actually parse
differently.
01​:22 <@​jnthn> But should be behaviourly equivalent.
01​:22 <@​jnthn> So, Rakudo bug.

From @masak

On Tue May 26 16​:24​:25 2009, jnthn@​jnthn.net wrote​:

01​:21 <@​jnthn> rakudo​: my %h = B => 2; my $x = "ABC"; $x .=
subst(/(<[BD]>)/,
{%h{$0}},​:global); say $x;
01​:21 < p6eval> rakudo 695300​: OUTPUT«A2C␤»
01​:21 <@​jnthn> rakudo​: my %h = B => 2; my $x = "ABC"; $x.=subst(/(<[BD]>)/,
{%h{$0}},​:global); say $x;
01​:21 < p6eval> rakudo 695300​: OUTPUT«Use of uninitialized value␤Use of
uninitialized value␤AC␤»
01​:21 <@​jnthn> Nailed it.
01​:21 < DanielC> spaces?
01​:22 <@​jnthn> DanielC​: Bit more to it than that. Those two actually parse
differently.
01​:22 <@​jnthn> But should be behaviourly equivalent.
01​:22 <@​jnthn> So, Rakudo bug.

At this point, $/ doesn't work well in subst-closures. However, the real cause for the RT
ticket has been fixed​:

$ perl6 -e 'my %h = B => 2; my $x = "ABC"; $x .= subst(/(<[BD]>)/, %h<B>, :global); say
$x;'
A2C

$ perl6 -e 'my %h = B => 2; my $x = "ABC"; $x.=subst(/(<[BD]>)/, %h<B>, :global); say $x;'
A2C

Resolving ticket.

The RT System itself - Status changed from 'new' to 'open'

@masak - Status changed from 'open' to 'resolved'