Hi Steve (2009.04.14_15:33:33_+0200)
> This assumes that the brightness is actually being handled the standard
> way, with hal and gnome-power-manager.  I'm not sure this is the case; I
> can't reproduce such a "wrap-around" behavior on my hardware, so I
> suspect this is happening outside of hal's control.

Yes, that it is going through gnome-power manager. Example debugging output:

 - Event0 0x1f20b70
TI:17:03:03	TH:0x1cbfa00	FI:gpm-button.c	FN:gpm_button_filter_x_events,149
 - Key 233 mapped to key brightness-up
TI:17:03:03	TH:0x1cbfa00	FI:gpm-button.c	FN:gpm_button_emit_type,96
 - emitting button-pressed : brightness-up
TI:17:03:03	TH:0x1cbfa00	FI:gpm-manager.c	FN:button_pressed_cb,1029
 - Button press event type=brightness-up
TI:17:03:03	TH:0x1cbfa00	FI:gpm-srv-screensaver.c	FN:button_pressed_cb,167
 - Button press event type=brightness-up
TI:17:03:03	TH:0x1cbfa00	FI:gpm-backlight.c	FN:gpm_backlight_button_pressed_cb,534
 - Button press event type=brightness-up
TI:17:03:03	TH:0x1cbfa00	FI:gpm-brightness-xrandr.c	FN:gpm_brightness_xrandr_foreach_screen,407
 - using resource 0x1f283d0
TI:17:03:03	TH:0x1cbfa00	FI:gpm-brightness-xrandr.c	FN:gpm_brightness_xrandr_foreach_resource,368
 - resource 1 of 4
TI:17:03:03	TH:0x1cbfa00	FI:gpm-brightness-xrandr.c	FN:gpm_brightness_xrandr_foreach_resource,368
 - resource 2 of 4
TI:17:03:03	TH:0x1cbfa00	FI:gpm-brightness-xrandr.c	FN:gpm_brightness_xrandr_output_up,280
 - hard value=296, min=0, max=296
TI:17:03:03	TH:0x1cbfa00	FI:gpm-brightness-xrandr.c	FN:gpm_brightness_xrandr_output_up,282
 - already max
TI:17:03:03	TH:0x1cbfa00	FI:gpm-brightness-xrandr.c	FN:gpm_brightness_xrandr_foreach_resource,368
 - resource 3 of 4
TI:17:03:03	TH:0x1cbfa00	FI:gpm-brightness-xrandr.c	FN:gpm_brightness_xrandr_foreach_resource,368
 - resource 4 of 4
TI:17:03:03	TH:0x1cbfa00	FI:gpm-brightness-xrandr.c	FN:gpm_brightness_xrandr_foreach_screen,407
 - using resource 0x1f283d0
TI:17:03:03	TH:0x1cbfa00	FI:gpm-brightness-xrandr.c	FN:gpm_brightness_xrandr_foreach_resource,368
 - resource 1 of 4
TI:17:03:03	TH:0x1cbfa00	FI:gpm-brightness-xrandr.c	FN:gpm_brightness_xrandr_foreach_resource,368
 - resource 2 of 4
TI:17:03:03	TH:0x1cbfa00	FI:gpm-brightness-xrandr.c	FN:gpm_brightness_xrandr_output_get_percentage,223
 - hard value=296, min=0, max=296
TI:17:03:03	TH:0x1cbfa00	FI:gpm-brightness-xrandr.c	FN:gpm_brightness_xrandr_output_get_percentage,225
 - percentage 100
TI:17:03:03	TH:0x1cbfa00	FI:gpm-brightness-xrandr.c	FN:gpm_brightness_xrandr_foreach_resource,368
 - resource 3 of 4
TI:17:03:03	TH:0x1cbfa00	FI:gpm-brightness-xrandr.c	FN:gpm_brightness_xrandr_foreach_resource,368
 - resource 4 of 4
TI:17:03:03	TH:0x1cbfa00	FI:gpm-feedback-widget.c	FN:gpm_feedback_display_value,169
 - Displaying 1.000000 on feedback widget
TI:17:03:03	TH:0x1cbfa00	FI:gpm-info.c	FN:button_pressed_cb,679
 - Button press event type=brightness-up
TI:17:03:03	TH:0x1cbfa00	FI:gpm-button.c	FN:hal_device_condition_cb,413
 - condition=ButtonPressed, details=brightness-up
TI:17:03:03	TH:0x1cbfa00	FI:gpm-button.c	FN:gpm_button_emit_type,92
 - ignoring duplicate button brightness-up
TI:17:03:03	TH:0x1cbfa00	FI:gpm-brightness-xrandr.c	FN:gpm_brightness_xrandr_filter_xevents,545
 - Event0 0x1f20b70