Thanks for your reply! I'm just here to say that I figured out (sort of) what was causing the problem ...

my $mw = MainWindow->new();
my $widget = $mw->SomeWidget(\%some_options)->pack()->focus();
&add_edit_popup($mw, $widget);
$mw->MainLoop;
[download]

This will fail. However ...

my $mw = MainWindow->new();
my $widget = $mw->SomeWidget(\%some_options)->pack();
&add_edit_popup($mw, $widget);
$mw->MainLoop;
[download]

This will succeed. The difference is not placing the focus() call in the declaration of the widget. If you do it later in the code using ...

$widget->focus();

Then you're golden!

I'm sure there's a perfectly good explanation for this behavior. What that might be is beyond my Perl knowledge.

Anyway, BIG thanks to all for your help!