How do I disable these warnings?

In theory, the following should work:

use PerlIO::encoding;
$PerlIO::encoding::fallback = Encode::FB_DEFAULT;
[download]

However, when I try it, for example

#!/usr/bin/perl
use PerlIO::encoding;
$PerlIO::encoding::fallback = Encode::FB_DEFAULT;

open my $fh, "<:encoding(UTF-8)", $ARGV[0] or die $!;

binmode STDOUT, ":encoding(UTF-8)";

while (<$fh>) { print }
[download]

with an input file such as  (where the 'ä' is Latin-1 encoded)

foo
bär
[download]

although it does silence the warning, I do get an endless loop!

foo
b�r
foo
b�r
foo
b�r
...

Not sure why...   (Encode::FB_QUIET, OTOH, doesn't have the latter problem).

Looks like a bug to me.  Can others confirm the problem?