You must be using windows, because on linux

#!/usr/bin/perl
use warnings;
use strict;

print STDERR "STDERR oops\n";
print STERR "STERR oops\n";
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gives

Name "main::STERR" used only once: possible typo at ./z8a line 7.
STDERR oops
print() on unopened filehandle STERR at ./z8a line 7.
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