Unable to change Backlight level while using Nvidia driver

[Norbert]

I have Sony VAIO F13Z1R laptop with discrete Nvidia GT425M:
01:00.0 VGA compatible controller: NVIDIA Corporation GF108M [GeForce GT 425M] (rev a1)

On fresh Ubuntu 13.10 (or 13.10 GNOME) I'm unable to change backlight level while using Nvidia 304 driver (304.88-0ubuntu8).
I see backlight desktop indicator, it reacts on fn+backlight keys, but level is not changed.

Nouveau driver controls my backlight level normally.

ProblemType: Bug
DistroRelease: Ubuntu 13.10
Package: nvidia-current 304.88-0ubuntu8
ProcVersionSignature: Ubuntu 3.11.0-12.19-generic 3.11.3
Uname: Linux 3.11.0-12-generic i686
NonfreeKernelModules: nvidia
ApportVersion: 2.12.5-0ubuntu2
Architecture: i386
Date: Mon Oct 21 14:01:54 2013
InstallationDate: Installed on 2013-10-20 (0 days ago)
InstallationMedia: Ubuntu 13.10 "Saucy Salamander" - Release i386 (20131016.1)
MarkForUpload: True
SourcePackage: nvidia-graphics-drivers-304
UpgradeStatus: No upgrade log present (probably fresh install)

[Norbert (nrbrtx)]

Screen resolution is correct (full-hd 1920x1080).
Backlight control works after manually creation of /etc/X11/xorg.conf by nvidia-xconfig and adding
{
Option "RegistryDwords" "EnableBrightnessControl=1"
}
to the Device section.