I haven't found an actual "fix" but from experiencing the same problem I've figured out that if you activate the classic app you're wanting to switch to by clicking on its icon in the dock, your cursor will almost always be visible. (For me, the cursor disappears when I click on a classic app window or other element to make it active instead of the dock icon.) Still a pain in the ass, though, so hopefully this will be fixed with 10.1.