Hi tye++

Many thanks for the thoughtful response. What you say makes sense, and I will follow-up with Rocco Caputo (POE) and Slaven Rezic (Tk) to see if we can figure out this issue.

BTW: I was able to eliminate the "Free non-Callback" problem by changing the use POE command to be use POE qw (Loop::TkActiveState);

Here is the latest version & output...

mactst.pl:

use warnings;
use strict;

use Tk;

use POE qw (Loop::TkActiveState);

if(! defined($poe_main_window)) {
    warn "\$poe_main_window not defined";
}
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Working command:

$ /usr/local/ActivePerl-5.14/bin/perl -c mactst.pl
mactst.pl syntax OK
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Non-working command:

$ /usr/local/ActivePerl-5.20/bin/perl -c mactst.pl
mactst.pl syntax OK
. (1):
 0 0x1030c4968   IV f=00000001 undef(1)
SV = IV(0x1030c4958) at 0x1030c4968
  REFCNT = 1
  FLAGS = ()
  IV = 0
Abort
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