Java Portable unable to use next-gen Java plugin?

I was looking through my Java settings to make sure that Seamonkey was using Java off the thumb drive and not off of C: and when I did, I noticed that it was still running the old version of the Java plugin. I tried changing it to the new one, and it told me that it would be unable to change because I had a browser window open.

So I closed Seamonkey and made sure that it was closed by checking Processes in Task Manager. I tried it again though, and it still told me I had a browser open, which I didn't. Is this a bug in Java Portable or did I mess something up?

To see what I mean, here's a link to a page about it off of Sun.

http://www.java.com/en/download/help/new_plugin.xml