We are seeing this same issue in our production 5.0 environment and test 5.1.2 envionrment. Our clients connect on with the view client on either Windows XP or 7 64 bit running on Optiplex 960 and have either 2 or 3 monitors.
The problem is so random it is hard to troubleshoot. One thing I've noticed if you move the mouse to the upper left hand corner of their primary screen the cursor will switch back to normal.