Add the -exportselection => 0 option to all listboxes. 
#need exportselection=>0 for using multiple selection boxes

my $lb0 = $mw->Listbox(-selectmode => 'extended',
                       -exportselection=> 0 )->pack;

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In reply to Re: simultaneous selections in Tk by zentara
in thread simultaneous selections in Tk by momo33

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