I can't explain the error that you're getting effectively, it seems that there's a widget event associated with the mouse left button release click. Here is another way to do it...by using a "scrolled Listbox" and by double clicking on a month you can get its corresponding value printed to the console, also you can do the same from clicking the button as you've originally intended:

#!/usr/local/bin/perl
use strict;
use warnings;
use Tk;

my $mainWindow = MainWindow->new(-title=>"Main Window");
my $listBox = $mainWindow->Scrolled(
   'Listbox',
   -scrollbars=>'e'
   )->pack;
$listBox->insert('end',qw(Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov
+ Dec));

$listBox->bind('<Double-1>', \&getActive);
$mainWindow->Button(
                    -text=>'print value',
                    -command=>\&getActive,
                    )->pack();

sub getActive{
    my $month;
    $month = $listBox->get('active');  #detects a selected list item
    print  $month,"\n";
    };
    

MainLoop;
[download]

Update: On closer inspection, why do you want to destroy the frame "$top_f" since it contains the widget that lets you browse the months collection?

my $button=$top->Button(
   -text=>'Print Value',
   -command => \&printMonth,
   #-relief=>'raised'
   )->pack();
   
sub printMonth{
    print "The Current Month is $month\n";
    }
[download]