McDarren reported a segfault in 5.8.4. It's something strange. This segfaults:

use warnings; use strict;
our $I = "f";
$I = undef; 
open $I, '<', \3 or die "open in mem: $!";
bless \$a, 0;
$I = ref \$a;
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But this doesn't:

use warnings; use strict;
our $I = "f";
undef $I;           ## <---
open $I, '<', \3 or die "open in mem: $!";
bless \$a, 0;
$I = ref \$a;
[download]

Fixed version follows: I've updated the OP.