I can also verify this on Thinkpad T23. It may be related to a recent ACPI update. There are issues when manipulating /proc/acpi/ibm/brightness directly.
|-/proc/acpi/ibm-|
root@mercury$ cat /proc/acpi/ibm/brightness
level: 2
commands: up, down
commands: level <level> (<level> is 0-7)
|-/proc/acpi/ibm-|
root@mercury$ echo up > /proc/acpi/ibm/brightness
|-/proc/acpi/ibm-|
root@mercury$ cat /proc/acpi/ibm/brightness
level: 0
commands: up, down
commands: level <level> (<level> is 0-7)
|-/proc/acpi/ibm-|
root@mercury$ echo up > /proc/acpi/ibm/brightness
|-/proc/acpi/ibm-|
root@mercury$ cat /proc/acpi/ibm/brightness
level: 1
commands: up, down
commands: level <level> (<level> is 0-7)
|-/proc/acpi/ibm-|
root@mercury$ echo up > /proc/acpi/ibm/brightness
|-/proc/acpi/ibm-|
root@mercury$ cat /proc/acpi/ibm/brightness
level: 2
commands: up, down
commands: level <level> (<level> is 0-7)
|-/proc/acpi/ibm-|
root@mercury$ echo up > /proc/acpi/ibm/brightness
|-/proc/acpi/ibm-|
root@mercury$ cat /proc/acpi/ibm/brightness
level: 1
commands: up, down
commands: level <level> (<level> is 0-7)
|-/proc/acpi/ibm-|
root@mercury$ echo level 7 > /proc/acpi/ibm/brightness
|-/proc/acpi/ibm-|
root@mercury$ cat /proc/acpi/ibm/brightness
level: 7
commands: up, down
commands: level <level> (<level> is 0-7)
|-/proc/acpi/ibm-|
root@mercury$ echo level 7 > /proc/acpi/ibm/brightness
|-/proc/acpi/ibm-|
root@mercury$ echo level 6 > /proc/acpi/ibm/brightness
|-/proc/acpi/ibm-|
root@mercury$ cat /proc/acpi/ibm/brightness
level: 6
commands: up, down
commands: level <level> (<level> is 0-7)
|-/proc/acpi/ibm-|
root@mercury$ echo level 7 > /proc/acpi/ibm/brightness
|-/proc/acpi/ibm-|
root@mercury$ cat /proc/acpi/ibm/brightness
level: 1
commands: up, down
commands: level <level> (<level> is 0-7)
I can also verify this on Thinkpad T23. It may be related to a recent ACPI update. There are issues when manipulating /proc/acpi/ ibm/brightness directly.
|-/proc/acpi/ibm-| ibm/brightness ibm/brightness ibm/brightness ibm/brightness ibm/brightness ibm/brightness ibm/brightness ibm/brightness ibm/brightness ibm/brightness ibm/brightness ibm/brightness ibm/brightness ibm/brightness ibm/brightness ibm/brightness
root@mercury$ cat /proc/acpi/
level: 2
commands: up, down
commands: level <level> (<level> is 0-7)
|-/proc/acpi/ibm-|
root@mercury$ echo up > /proc/acpi/
|-/proc/acpi/ibm-|
root@mercury$ cat /proc/acpi/
level: 0
commands: up, down
commands: level <level> (<level> is 0-7)
|-/proc/acpi/ibm-|
root@mercury$ echo up > /proc/acpi/
|-/proc/acpi/ibm-|
root@mercury$ cat /proc/acpi/
level: 1
commands: up, down
commands: level <level> (<level> is 0-7)
|-/proc/acpi/ibm-|
root@mercury$ echo up > /proc/acpi/
|-/proc/acpi/ibm-|
root@mercury$ cat /proc/acpi/
level: 2
commands: up, down
commands: level <level> (<level> is 0-7)
|-/proc/acpi/ibm-|
root@mercury$ echo up > /proc/acpi/
|-/proc/acpi/ibm-|
root@mercury$ cat /proc/acpi/
level: 1
commands: up, down
commands: level <level> (<level> is 0-7)
|-/proc/acpi/ibm-|
root@mercury$ echo level 7 > /proc/acpi/
|-/proc/acpi/ibm-|
root@mercury$ cat /proc/acpi/
level: 7
commands: up, down
commands: level <level> (<level> is 0-7)
|-/proc/acpi/ibm-|
root@mercury$ echo level 7 > /proc/acpi/
|-/proc/acpi/ibm-|
root@mercury$ echo level 6 > /proc/acpi/
|-/proc/acpi/ibm-|
root@mercury$ cat /proc/acpi/
level: 6
commands: up, down
commands: level <level> (<level> is 0-7)
|-/proc/acpi/ibm-|
root@mercury$ echo level 7 > /proc/acpi/
|-/proc/acpi/ibm-|
root@mercury$ cat /proc/acpi/
level: 1
commands: up, down
commands: level <level> (<level> is 0-7)