I've knocked up this little app. which inserts ten items into the listbox every time you hit the <Insert> button. It seems to update the scroll bar ok on my system, Sun Ultra 30, Solaris 9, perl 5.8.4, Tk-804.027.

use strict;
use warnings;

use Tk;

my $rcGetTen = do
   {
       my $count = 0;
       sub
       {
           my @arr;
           push @arr, q{Item } . ++ $count
              for 1 .. 10;
           return @arr;
       };
   };

my $bgColour = q{LightSteelBlue3};
my %labelColours =
   (
      -foreground => q{NavyBlue},
      -background => q{LemonChiffon}
   );
my %buttonColours =
   (
      -background         => q{grey35},
      -foreground         => q{yellow2},
      -activebackground   => q{grey45},
      -activeforeground   => q{yellow},
      -disabledforeground => q{grey55}
   );
my %commonListboxOpts =
   (
      -setgrid          => 1,
      -scrollbars       => q{e},
      -selectmode       => q{single},
      -selectforeground => q{grey35},
      -selectbackground => q{AntiqueWhite},
      -exportselection  => 0
   );

my $mainWin = MainWindow->new( 
   -background  => $bgColour,
   );
$mainWin->title(q{scrollListbox});

my $listboxFrame = $mainWin->Frame(
   -relief      => q{flat},
   -background  => $bgColour,
   -borderwidth => 2,
   );
$listboxFrame->pack(
   -side => q{top},
   );
my $listbox = $listboxFrame->Scrolled(
   q{Listbox},
   %commonListboxOpts,
   -width   => 15,
   -height  => 6,
   -setgrid => 1,
   );
$listbox->pack(
   -padx   => 5,
   -pady   => 5,
   -fill   => q{y},
   -expand => 1,
   -anchor => q{n},
   );

my $controlButtonFrame = $mainWin->Frame(
   -relief      => q{flat},
   -background  => $bgColour,
   -borderwidth => 2,
   );
$controlButtonFrame->pack(
   -side => q{top},
   );
my $quitButton = $controlButtonFrame->Button(
   %buttonColours,
   -width   => 6,
   -text    => q{Quit},
   -command => sub {exit;},
   );
$quitButton->pack(
   -side => q{right},
   -padx => 5,
   -pady => 5,
   );
my $insertButton = $controlButtonFrame->Button(
   %buttonColours,
   -width   => 6,
   -text    => q{Insert},
   -command => sub { $listbox->insert( q{end}, $rcGetTen->() ) },
   );
$insertButton->pack(
   -side => q{right},
   -padx => 5,
   -pady => 5,
   );

MainLoop();
[download]

I hope this is of interest.

Cheers,

JohnGG