From @ShimmerFairy

<labster> r​: my $a = 'gfoo'; $a ~~ s@​gf@​f@​;
<p6eval> rakudo 897636​: OUTPUT«===SORRY!===␤Variable '@​f' is not
declared␤at /tmp/hTstr3dCxL​:1␤------> my $a = 'gfoo'; $a ~~ s@​gf@​f⏏@​;␤»

<lue> r​: my $a = "gfoo"; $a ~~ s^gf^f^; say $a;
<p6eval> ..rakudo 897636​: OUTPUT«===SORRY!===␤Unrecognized regex
metacharacter ; (must be quoted to match literally)␤at
/tmp/a5KNf0HcNh​:1␤------> my $a = "gfoo"; $a ~~ s^gf^f^⏏; say
$a;␤Couldn't find terminator $stop␤at /tmp/a5KNf0HcNh​:1␤------> my $a = "g…

It would seem that characters which hold some meaning in regexes can't
be used to delimit substitutions.

From @FROGGS

Fix​: Raku/nqp@c3cdeb6e37
Test​: Raku/roast@83871378dd

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

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