use warnings;
use diagnostics;
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gives a clue:

Variable "$list_ref" will not stay shared at - line 15 (#1)
    (W closure) An inner (nested) named subroutine is referencing a
    lexical variable defined in an outer subroutine.
    
    When the inner subroutine is called, it will probably see the valu
+e of
    the outer subroutine's variable as it was before and during the *f
+irst*
    call to the outer subroutine; in this case, after the first call t
+o the
    outer subroutine is complete, the inner and outer subroutines will
+ no
    longer share a common value for the variable.  In other words, the
    variable will no longer be shared.
    
    Furthermore, if the outer subroutine is anonymous and references a
    lexical variable outside itself, then the outer and inner subrouti
+nes
    will never share the given variable.
    
    This problem can usually be solved by making the inner subroutine
    anonymous, using the sub {} syntax.  When inner anonymous subs tha
+t
    reference variables in outer subroutines are called or referenced,
+ they
    are automatically rebound to the current values of such variables.
[download]

_($_=" "x(1<<5)."?\n".q·/)Oo.  G°\        /
                              /\_¯/(q    /
----------------------------  \__(m.====·.(_("always off the crowd"))."·
");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}