I hate to necro old posts but I have the same issue.
But I use Arch and have had this on KDE 4.9 and 4.10 RCs. Probably 4.8 too.
Just like the reporter my cursor corrupts on the line between my screen 1 and screen 2.
For me everytime it happens it is corrupt on screen 1 and just fine on screen 2.
I hate to necro old posts but I have the same issue.
But I use Arch and have had this on KDE 4.9 and 4.10 RCs. Probably 4.8 too.
Just like the reporter my cursor corrupts on the line between my screen 1 and screen 2.
For me everytime it happens it is corrupt on screen 1 and just fine on screen 2.