Hmm... I've experienced this problem before, but with a browser. I solve it by refreshing the page, like moving around the file for it to update, or turn on&off the monitor.
Although it may also be a package conflict with another package, so what you might want to try is to un-install all your packages, and see if that solves the problem. If it doesn't then you can re-install them all and, could you please give us your system details? Maybe so that John can reproduce the issue.