Backlight cannot be controlled after logging out and relogin

I am using Version 12.10 and Samsung 300V5A laptop.

The brightness could not be changed until I modify grub setting from /etc/default/grub and modifying the line as follows:

"GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_osi=Linux acpi_backlight=vendor"

Now it works, but when I need to logout and login again, it cannot be controlled again.

The only solution was restarting...

Then I found intel-gpu-tools. Now without restarting I can write sudo intel_backlight 100 and it increases the brightness again.

Do you know why it works at first boot, but not after logout & relogin? Typing the command above in every 10 minutes after leaving computer alone is so annoying.

Thanks.

ProblemType: Bug
DistroRelease: Ubuntu 12.10
Package: acpi (not installed)
ProcVersionSignature: Ubuntu 3.5.0-25.39-generic 3.5.7.4
Uname: Linux 3.5.0-25-generic x86_64
ApportVersion: 2.6.1-0ubuntu10
Architecture: amd64
Date: Sun Mar 10 23:30:59 2013
InstallationDate: Installed on 2013-02-18 (20 days ago)
InstallationMedia: Kubuntu 12.10 "Quantal Quetzal" - Release amd64 (20121017.1)
MarkForUpload: True
SourcePackage: acpi
UpgradeStatus: No upgrade log present (probably fresh install)

ProblemType: Bug
DistroRelease: Ubuntu 12.10
Package: acpi 1.6-1
ProcVersionSignature: Ubuntu 3.5.0-25.39-generic 3.5.7.4
Uname: Linux 3.5.0-25-generic x86_64
ApportVersion: 2.6.1-0ubuntu10
Architecture: amd64
Date: Sun Mar 17 15:18:12 2013
InstallationDate: Installed on 2013-02-18 (26 days ago)
InstallationMedia: Kubuntu 12.10 "Quantal Quetzal" - Release amd64 (20121017.1)
MarkForUpload: True
SourcePackage: acpi
UpgradeStatus: Upgraded to quantal on 2013-03-15 (2 days ago)