JNLP update question

Question about JNLP distribution, which I am quite new to.

I've noticed that when I update one of my jars on the server, and then open my JNLP site again, it does not update and just runs the old version. Usually I have to go into my java settings and delete the old JNLP. This is a pain and will prevent people from getting the latest version. Sometimes it does update, usually if there's a long period of time (days) between the old and new versions.

Supposedly it should go off the file timestamp - but either my server doesn't timestamp properly or that isn't working too well. I know there's a whole XML versioning system, at first look it seems like overkill.

What am I missing?

If I remember correctly, I use something like this (and updates the version each time):

<jar href="Demo.jar" main="true" version="1.01"/>

are you behind a proxy server which caches things maybe ?