brightness changes 2 levels at once

Binary package hint: gnome-power-manager

here is picture of what happens:
1) I set brightness to 0 level:
levels: 0 1 2 3 4 5 6 7 8
current: 0

2) I press brightness up once:
levels: 0 1 2 3 4 5 6 7 8
current: 2

3) ... once more:
levels: 0 1 2 3 4 5 6 7 8
current: 4

4) ... and once more:
levels: 0 1 2 3 4 5 6 7 8
current: 6

and same for brightness down.
Now I do killall gnome-power-manager, and then repeat test:
1) from 0 level, brightness up once:
levels: 0 1 2 3 4 5 6 7 8
current: 1

2) ... once more:
levels: 0 1 2 3 4 5 6 7 8
current: 2

3) ... and once more:
levels: 0 1 2 3 4 5 6 7 8
current: 3

This is correct behavior, when g-p-m is not running.

gnome-power-manager --debug --verbose --no-daemon produces no output, so no logs to attach

ProblemType: Bug
Architecture: amd64
Date: Wed Oct 21 21:33:23 2009
DistroRelease: Ubuntu 9.10
Package: gnome-power-manager 2.28.1-0ubuntu1
ProcEnviron:
 PATH=(custom, user)
 LANG=ru_RU.UTF-8
 SHELL=/bin/bash
ProcVersionSignature: Ubuntu 2.6.31-14.48-generic
SourcePackage: gnome-power-manager
Uname: Linux 2.6.31-14-generic x86_64
XsessionErrors:
 (gnome-settings-daemon:19958): GLib-CRITICAL **: g_propagate_error: assertion `src != NULL' failed
 (nautilus:20044): Eel-CRITICAL **: eel_preferences_get_boolean: assertion `preferences_is_initialized ()' failed
 (polkit-gnome-authentication-agent-1:20069): GLib-CRITICAL **: g_once_init_leave: assertion `initialization_value != 0' failed
 (gnome-panel:20043): Gdk-WARNING **: /build/buildd/gtk+2.0-2.18.3/gdk/x11/gdkdrawable-x11.c:952 drawable is not a pixmap or window
 (gnome-panel:20043): Gtk-WARNING **: gtk_widget_size_allocate(): attempt to allocate widget with width -5 and height 24