1. The simple solution. Each ComboBox can be configured as either
   • -dropdown, which allow edits, or
   • -dropdownlist, which does not allow edits.
   Of the two, only -dropdown has the split focus issue. So, if you can just use -dropdownlist, then your problem is solved.
2. The less-simple solution. You can use Win32::API to call GetComboBoxInfo, which will give you the handles to the component controls. You can do this with straight-forward procedural code, but I chose to create a sub-class that provides the new methods GetEditControl and GetDropDownControl.

Working, tested code:

package Win32::GUI::Combobox_improved;
use strict;
use warnings;
use Win32::GUI;
use Win32::API;
our @ISA = qw( Win32::GUI::Combobox );

# API GetComboBoxInfo:
#   http://msdn.microsoft.com/library/en-us/shellcc/platform/commctls/
+comboboxes/comboboxreference/comboboxfunctions/getcomboboxinfo.asp
# Struct COMBOINFO:
#   http://msdn.microsoft.com/library/en-us/shellcc/platform/commctls/
+comboboxes/comboboxreference/comboboxstructures/comboboxinfo.asp
# Struct RECT:
#   http://msdn.microsoft.com/library/en-us/gdi/rectangl_6cqa.asp

# Note: I have flattened the rcItem and rcButton RECT structs, 
# because of bugs in Win32::API and Win32::API::Struct's 
# handling of nested structs, or in my own understanding of it.
Win32::API::Struct->typedef( 'COMBOBOXINFO', qw(
    DWORD cbSize;
    LONG  rcItem_left;  
    LONG  rcItem_top;   
    LONG  rcItem_right; 
    LONG  rcItem_bottom;
    LONG  rcButton_left;  
    LONG  rcButton_top;   
    LONG  rcButton_right; 
    LONG  rcButton_bottom;
    DWORD stateButton;
    HWND  hwndCombo;
    HWND  hwndItem;
    HWND  hwndList;
));

Win32::API->Import("user32", <<'END_API') or die;
  BOOL GetComboBoxInfo(
    HWND           hwndCombo,
    COMBOBOXINFO * pcbi
  );
END_API

sub _GetComboBoxInfo {
  my ($self) = @_;
  my $hwndCombo = $self->{-handle};

  my $pcbi = Win32::API::Struct->new('COMBOBOXINFO');
  $pcbi->{cbSize} = $pcbi->sizeof();
  my $rc = GetComboBoxInfo(
      $hwndCombo,
      $pcbi,
  );
  return unless $rc;

  warn unless $hwndCombo == $pcbi->{hwndCombo};

  return $pcbi;
}

# Retrieves the handle to the child edit control 
# portion of a ComboBox control.
sub GetEditControl {
  my ($self) = @_;
  my $combo_box_info = $self->_GetComboBoxInfo()
    or return;
  return $combo_box_info->{hwndItem};
}

# Retrieves the handle to the child drop-down control
# portion of a ComboBox control.
sub GetDropDownControl {
  my ($self) = @_;
  my $combo_box_info = $self->_GetComboBoxInfo()
    or return;
  return $combo_box_info->{hwndList};
}


package main;
use strict;
use warnings;
use Win32::GUI;
$| = 1; # Important! - Turn off buffering

my $W1 = Win32::GUI::Window->new(
  -name  => 'W1',
  -title => 'PerlMonks_494615',
  -pos   => [ 100, 100 ],
  -size  => [ 300, 200 ],
);

my $combo_style = '-dropdown';     # Allows edits
#my $combo_style = '-dropdownlist'; # Does not allow edits

my $cb1 = Win32::GUI::Combobox_improved->new(
  $W1, # Parent
  -name         => 'CB1',
  -left         =>  10,
  -top          =>  10,
  -width        => 125,
  -height       => 100,
  -tabstop      =>   1,
  $combo_style  =>   1,
);
my $cb2 = Win32::GUI::Combobox_improved->new(
  $W1, # Parent
  -name         => 'CB2',
  -left         => 140,
  -top          =>  10,
  -width        => 125,
  -height       => 100,
  -tabstop      =>   1,
  $combo_style  =>   1,
);

{
  my %handle_to_parent;
  foreach my $cb ( $cb1, $cb2 ) {
    my $handle_cb   = $cb->{-handle};
    my $handle_edit = $cb->GetEditControl();
    my $handle_dd   = $cb->GetDropDownControl();
    $handle_to_parent{ $handle_cb   } = $handle_cb;
    $handle_to_parent{ $handle_edit } = $handle_cb;
    $handle_to_parent{ $handle_dd   } = $handle_cb;
  }
  my %handle_to_name = (
    $cb1->{-handle} => 'CB1',
    $cb2->{-handle} => 'CB2',
  );
  sub dump_it {
    my $event = (caller(1))[3];
    my $focus  = $W1->GetFocus();
    my $true_focus = $handle_to_parent{$focus} || $focus;
    my $name = $handle_to_name{$true_focus};
    print "$event: focus going to $name\n";
  }
}

$cb1->InsertItem($_) foreach qw(Able Baker Charlie);
$cb2->InsertItem($_) foreach qw(Roger Fox Dog);
$cb1->Select(0);
$cb2->Select(0);

$W1->Show();
Win32::GUI::Dialog();

sub CB1_GotFocus  {  dump_it() }
sub CB2_GotFocus  {  dump_it() }
sub CB1_LostFocus {  dump_it() }
sub CB2_LostFocus {  dump_it() }
[download]

Thanks!! That is the perfect solution to my problem and even included references for the internals. Again, thanks a lot! ++