This happened both under the open source driver and the Catalyst driver. I think it happens when the cursor switches from one monitor to the other but not every time. Maybe 1x every 2 weeks? It has happened 4 times at least.
Logging out does not fix it. Changing the cursor and its theme does not fix it.
Here’s what it looks like:
http://i.imgur.com/dKtanjg.jpg
Here’s someone experiencing the same thing on Ubuntu: https://bugs.launchpad.net/ubuntu/+source/xserver-xorg-video-ati/+bug/360724
Computer:
Linux 3.16.7-21-desktop
openSUSE 13.2 (Harlequin) (x86_64)
KDE 4.14.9
AMD A4-3400 APU with Radeon™ HD Graphics
The computer is the Acer AX1470-UR30P (Desktop)