Well, that solved a probable error, but it uncovered a more serious one. As I expected, there does indeed appear to be a problem with the passed hash. podmaster has mentioned (via CB) that this is probably the problem, and that I should pass a hashref instead, but I haven't figured that out just yet. Here's a new dump...

[jason@lappy jason]$ perl test_menu.pl 
$VAR1 = bless( {
                 '1' => undef,
                 '2' => undef,
                 '3' => undef,
                 '_header' => 'Just testing...',
                 '4' => undef,
                 '_comment' => 'Ok, this is where the comment section 
+would normally go.',
                 '_title' => 'Testing menu'
               }, 'Menu' );
[download]

Update: Thanks to podmaster who pointed out that set_choices() should have {}'s in the HoH assignment, rather than ()'s. Thanks everyone!