Just a tidbit of a thought...... IIRC, the last time I experimented with cut-n-paste sort of things, the most reliable in my testing was the Tk::Text widget. The biggest glitch was when copying, did it automatically get the text into both the mouse-paste-clipboard, as well as the menu paste selection( control-v). See Tk copy to mouse clipboard

Also I found using Tk in a withdrawn state, gave good results

#!/usr/bin/perl
use warnings;
use strict;
use Tk;
use Tk::Clipboard;

my $mw = tkinit;
$mw->withdraw;  #use Tk without showing a window

my $content = 'foobar'.time;

print "$content\n";

$mw->clipboardClear;
$mw->clipboardAppend($content);

MainLoop;
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