I'm not sure if this is it (since I don't have 5.004_01 around), but this is what I think is happening.

This code works (it's bad for many reasons, but it works):

open (TEST,"test") || die $!;
mysub (TEST);

sub mysub {
my $fh = shift;
print $fh;
my $txt = <$fh>;
print $txt;
}
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as does this

package mypac;
sub mysub {
my $fh = shift;
print $fh;
my $txt = <$fh>;
print $txt;
}

package main;
open (TEST,"test") || die $!;
mypac::mysub ("main::TEST");
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The line mysub (TEST) is called like mysub ("TEST"). When using a filehandle, you can use a string instead of the filehandle (which is the  my $txt = <$fh>). I'm guessing that perl 5.004_01 had a shared namespace for filehandles, and later versions of perl do not.