Just a guess, but I'm betting you have a focus problem. Try clicking the mouse in the entry first, or tabbing around. Try adding $f->focus to force the last entry to have focus. You might want to name your entries better, like $f{'Name'} so you can assign focus order better.

Some code to show what happens:

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

#changes focus on Return(Enter) key but not Tab

my $win = MainWindow->new();

 my $foo = $win->Entry->pack;
 my $bar = $win->Entry->pack;
 my $baz = $win->Entry->pack;
 my $boo = $win->Entry->pack;
 my $baa = $win->Entry->pack;

&defineOrder($foo,$baa,$bar,$boo,$baz);

sub defineOrder_old
{
    my $widget;
    for (my $i=0; defined( $_[$i+1] ); $i++)
    {
      $_[$i]->bind('<Key-Return>', [\&focus, $_[$i+1]]);
      
      
      # won't work with Tab
      $_[$i]->bind('all', '<Tab>', [\&focus, $_[$i+1]]);
    }

    # Uncomment this line if you want to wrap around
    $_[$#_]->bind('<Key-Return>',  [\&focus, $_[0]]);

    $_[0]->focus;
}


sub defineOrder
{
    my $widget;
    for (my $i=0; defined( $_[$i+1] ); $i++)
    {
      $_[$i]->bind( '<Key-Return>', [\&focus, $_[$i+1]]);
      $_[$i]->bind( '<Tab>', [\&focus, $_[$i+1]]);
    }

    # Uncomment this line if you want to wrap around
    $_[ $#_ ]->bind('<Key-Return>',  [\&focus, $_[0]]);
    $_[ $#_ ]->bind('<Tab>',  [\&focus, $_[0]]);

    $_[0]->focus;
}




sub focus
{
    my ($tk, $self) = @_;
    $self->focus;
}

MainLoop();
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