Maybe this comment is not a comment indeed. It may be inside a larger quote construct that does interpolation, like

my $a = "

# this is a comment, but not really (with $interpolation)

$a = 3

";
print $a
[download]

printf <<PERL, "not";

for (@html) { pretty_print($_) }

# a comment is %s always a $comment
# subtler because of here-docs

PERL
[download]

Any of these would trigger similar warnings, due to the unitialized contents in $interpolation, $a and $comment.