WebStart errors and Temporary Internet Files Setting

I've been working on a WebStart application for a few weeks and today it started failing to start. An error was raised about one of the jar files not being signed. I checked the jar and it was signed!

Turned out the error was down to a javaws setting (run 'javaws - viewer' to see the settings).

For some reason the 'Keep Temporary files on my computer' setting was not enabled. I read on various other forums that this had caused similar problems for other people. I enabled the setting, pressed deleted files just incase anything was hanging around and then started my application, it worked :)

So I'm puzzled as to how the setting became disabled as I did not do it. I'm also puzzled why this should cause the problem I was seeing, it seems to have happened to other people to so its not a one off. Some people reported the problem back in 1.4 Java, I'm running the latest 1.6.