Just so you get a clearer picture of how packing works, try this: Put your Exit button first in the packing in your buildBUI sub, and it will now be the last thing to be chopped off. Of course your frames gets squished instead.

sub buildGui {
  $goMainWindow = new MainWindow;

#pack your Exit button first in the list
   my ($oExit) = $goMainWindow->Button(-text => 'Exit',
                      -command => sub{exit},
                     )->pack(
                      -padx => '5',
                      -pady => '5',
                      -side => 'bottom',
                     );


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