Status update. I think I've fixed the problem. My laptop has an ATI graphics card. When I was using Dapper, I had enabled hardware 3D acceleration by using the ATI proprietaty driver. When I upgraded to Edgy, I lost the 3D support because the configuration went back to using the open Ubuntu graphics driver. So I followed the steps under https://help.ubuntu.com/community/BinaryDriverHowto/ATI to re-enable the 3D support. After successfully re-enabling 3D graphics support, the intermitently appearing horizontal line below the cursor appears to have permanently stopped appearing.
-- [r100] cursor glitches when scanline is being updated https://launchpad.net/bugs/21545 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
