How are you using the file handle (specific code sample required here!)? The following works for me:

use strict;
use warnings;

my $str;
my $self = bless {};

open $self->{fh}, '>', \$str;

my $fh = $self->{fh}; # Perl gets confused unless globs are simple sca
+lars
print $fh "Hello world\n";
close $self->{fh};

print $str;
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Prints:

Hello world
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