I have a Asus N56v Laptop, recently upgraded to Vivid and now my Brightness Controls accessed via (FN+F5, FN+F6, FN+F5) have a dramatic lag. I can wait 30 up to 120 seconds before the keystroke is registered and the system adjusts.
I initially didn't think they were working at all, after spamming the keys it took 10 minutes to finish adjusting. The Volume keys configured the same way with fn+f10 work just fine and quickly.
This isn't the first time I have run into issues with the brightness controls either. They worked perfectly on Ubuntu 14.04 but stopped working all together in 14.10 and now they work but with extreme latency.
Any Ideas?