I’m having a strange problem with the cursor on 16.04 with my dual Radeon cards and 4 monitors. The cursor flickers when on the 2 monitors associated with the card running the primary screen. There is also a 2nd cursor on the primary screen that is only visible on the desktop after boot. It won’t appear on top of any windows or desktop items. The flickering only happens on the dual video card setup. I boot the drive off either a Macbook Pro, an Optiplex 990, or an Optiplex 980 during the day and the 990 with the dual cards is the only one it happens on.
In my opinion it’s a driver problem. Do you use the open source drivers?
Yes, I stayed with the open source drivers. Do you think it’s something that getting fglrx running would fix, or if it’s just more stable to be running Nvidia for dual card machines.
First of all you can make a bug post on the mesa page about your problem. You have 2 options
1/ W8 to amdgpu-pro to be release like i am 
2/ Use a older version like 14.04.x and use fglrx (in 16.04 it’s not available )