I also am having this problem
but it is not intermitent, every time I move the mouse over to one of clients the cursor stops moving. Clicking still works and if I use the client pc's mouse it still works. Using the bypass toggle temporarily returns control of the cursor to the main machine but if I stop the bypass the cursor is stuck on the client screen again. Also of note I do have a second alt pc which does not have any issues when passing the cursor. Systems being used: Mac mini running windows 7 on bootcamp, sony vaio (japanese) and a dell laptop both running xp.