Actually, the issue really is the use utf8 which allows you to use utf8 in your program identifiers. For instance:

use strict;
use warnings;
my %hash = ( asd => 1 );

sub ff {
  print utf8::is_utf8($_[0]) ? 1 : 0, "\n";
}

eval {
    use utf8;
    ff(%hash); # now prints 0
};
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I suppose it's reasonable that perl encodes barewords as utf8 if you use utf8 even if only ascii characters are involved.

Update: from the utf8 documentation:

The "use utf8" pragma tells the Perl parser to allow UTF-8 in the pro-
gram text in the current lexical scope (allow UTF-EBCDIC on EBCDIC
based platforms). ...

Do not use this pragma for anything else than telling Perl that your
script is written in UTF-8. The utility functions described below are
useful for their own purposes, but they are not really part of the
"pragmatic" effect.
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