Symptoms appeared after upgrading to BIOS ver: 4.0.11, A13 from previous ver: 4.0.9, A12 and clean-installing Ubuntu 16.10 or 16.04.1.
DELL Inspiron 14-3452 (3000 series) laptop
Upon tapping, once and releasing, either the XF86monBrightnessUp or XF86monBrightnessDown keys in a Unity-7 session, the OSD appears, sometimes delayed, and begins to lower or raise the backlight level, repeatedly, to the maximum or minimum level. The system comes under load and is less responsive to any input or attempts to cancel / counteract the action.
Manual adjustments via the echoing of numbers-in-range to the /sys/class/backlight/intel_backlight/brightness work normally and as expected.
*** SOLUTION ***
Revert to previous BIOS version: 4.0.9, A12
Brightness keys return to normal operation in all desktop/windowing environments.
cross-posted to: Laptop >> General Hardware / Video + OS and Applications - Forum