Comment 83 for bug 1007765

I am still having this problem even after adding 'acpi_backlight=vendor' to grub cmd option, but now crash occurs less often.
This problem also occurs when brightness changes due to power on/off. In this case(when frozen) if I remove or plug-in charger, brightness level changes but nothing else work.
Sometime I notice that Brightness Indicator doesn't display brightness level correctly.

Ubuntu 13.04 (64-bit), ATI Mobility Radeon HD 5400 series