do you know any workaround for this very long lasting bug buried somewhere in kernel or in gnome-power-manager, please? Thanks in advance. See description:
closed as too localized by Luis Alvarado♦ Mar 14 at 17:09
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as a workaround suggest the "brightness" applet in gnome
Seems to work fine on 11.04, with a Thinkpad T42.
The reason, as given above, is that the version of the thinkpad_acpi module that you have is not masking the brightness hotkeys correctly. This means that when you press a hotkey for brightness up or down, the bios grabs it, changes the brightness and also produces an ACPI event. The acpi drivers then generate a virtal keypress, something like X86FreeBrightnessUp, or whatever it is. The gnome power manager responds to this perceived keypress by increasing the brightness again.
Upgrade, or do a search for thinkpad_acpi hotkey mask and change the default mask to one that masks the brightness hotkeys.
You find similar issues for volume, though in that case it is due to the hardware and software mixers both being increased by the same button.