Simply resizing my browser window before pasting the second url seems to thwart this (But I don't have flash installed). Without flash, it falls firmly into the "kinda-works sometimes if everything goes perfect" camp.
So its another demonstration of flash being ridiculously insecure. These guys did it better, even defeating tor to reveal the origin IP. http://dl.packetstormsecurity.net/0610-advisories/Practical_...