The Tech Report spotted that a bug in ATI's Catalyst drivers can suddenly make the Windows mouse cursor double in size. The site explains the issue mainly occurs on Windows 7 systems with ATI Radeon HD 5000 series graphics cards. AMD is aware of the issue and says it will be fixed next month with Catalyst 9.11.
A visit to AMD's Game forums tells us the issue affects Radeon HD 5800-series cards, as well, and the new Catalyst 9.10 drivers don't seem to help. Users who complain typically run Windows 7, and some talk of multi-monitor setups, but they look to have little else in common—the problem seems to apply to certain DX11 Radeons running on both Intel and AMD platforms.
As far as we're aware, the only way to reset the cursor size is to either reboot or make the driver crash. The cursor size also stays normal if you run the Windows Magnifier in the background (without magnification actually enabled) or if you enable pointer trails. One forum user claims grabbing the latest AMD GPU Clock Tool and manually forcing the default clock speeds will do the trick, but that approach didn't work for us.