As bgcommon notes, the bug is easily triggered. Set your brightness to a certain level with the Brightness Applet. Alter the brightness with the [Fn + Up] or [Fn + Down] key. Close/reopen the laptop lid and the level will revert to that which had originally been set in the Brightness Applet.

As you requested, here are the results of the commands. The commands were executed after setting the brightness with the Brightness Applet but before using the [Fn + *] key:

gconftool -a /apps/gnome-power-manager/backlight
--------------------
 idle_dim_battery = true
 idle_brightness = 30
 dpms_method_battery = default
 dpms_method_ac = default
 idle_dim_time = 30
 brightness_battery = 70
 enable = true
 idle_dim_ac = false
 brightness_ac = 81
 battery_reduce = true


gnome-power-bugreport.sh
--------------------
Distro version:       DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=8.04
DISTRIB_CODENAME=hardy
DISTRIB_DESCRIPTION="Ubuntu 8.04"
Kernel version:       2.6.24-19-generic
g-p-m version:        2.22.1
HAL version:          0.5.11rc2
System manufacturer:  missing
System version:       missing
System product:       missing
AC adapter present:   yes
Battery present:      yes
Laptop panel present: yes
CPU scaling present:  yes
Battery Information:
  battery.charge_level.current = 50116  (0xc3c4)  (int)
  battery.charge_level.design = 53280  (0xd020)  (int)
  battery.charge_level.last_full = 50116  (0xc3c4)  (int)
  battery.charge_level.percentage = 100  (0x64)  (int)
  battery.charge_level.rate = 11  (0xb)  (int)
  battery.is_rechargeable = true  (bool)
  battery.model = ' DELLUD2657'  (string)
  battery.present = true  (bool)
  battery.rechargeable.is_charging = false  (bool)
  battery.rechargeable.is_discharging = false  (bool)
  battery.reporting.current = 4800  (0x12c0)  (int)
  battery.reporting.design = 4800  (0x12c0)  (int)
  battery.reporting.last_full = 4515  (0x11a3)  (int)
  battery.reporting.rate = 1  (0x1)  (int)
  battery.reporting.technology = 'Li-ion'  (string)
  battery.reporting.unit = 'mAh'  (string)
  battery.technology = 'lithium-ion'  (string)
  battery.type = 'primary'  (string)
  battery.vendor = 'SMP'  (string)
  battery.voltage.current = 12424  (0x3088)  (int)
  battery.voltage.design = 11100  (0x2b5c)  (int)
  battery.voltage.unit = 'mV'  (string)
GNOME Power Manager Process Information:
john      7017  0.0  1.1 247184 11636 ?        Ss   14:16   0:00 gnome-power-manager
john      7109  0.0  1.0 225616 10816 ?        S    14:17   0:00 /usr/lib/gnome-power-manager/gnome-brightness-applet --oaf-activate-iid=OAFIID:GNOME_BrightnessApplet_Factory --oaf-ior-fd=36
HAL Process Information:
107       5669  0.0  0.4  40208  4828 ?        Ss   14:13   0:03 /usr/sbin/hald
root      5735  0.0  0.1  22048  1316 ?        S    14:13   0:00  \_ hald-runner
root      5748  0.0  0.2  34628  2404 ?        S    14:13   0:00      \_ /usr/lib/hal/hald-addon-dell-backlight
root      5749  0.0  0.1  24156  1296 ?        S    14:13   0:00      \_ hald-addon-input: Listening on /dev/input/event8 /dev/input/event10 /dev/input/event9 /dev/input/event1 /dev/input/event4 /dev/input/event5 /dev/input/event6
root      5759  0.0  0.1  24168  1324 ?        S    14:13   0:00      \_ /usr/lib/hal/hald-addon-cpufreq
107       5760  0.0  0.1  16672  1044 ?        S    14:13   0:00      \_ hald-addon-acpi: listening on acpid socket /var/run/acpid.socket
root      5783  0.0  0.1  24156  1280 ?        S    14:13   0:00      \_ hald-addon-storage: polling /dev/scd0 (every 2 sec)