Agile Gadget doesn't work when using in Confluence or other Gadget containers

When adding the GH agile gadget to a confluence page it will display one chart the first time it's being viewed, but it will fail for any consecutive attempts.
Only after 2 hours it will work once and then stop to work again for two hours.

This issue is due a missing NO-CACHE header on the response of the gadget resource which generates the image.
Adding the header Cache-Control: NO-Cache will fix this problem.

GreenhopperRessource.java (IMHO: java class should be renamed to GreenhopperResource)
Line 129

return !errors.isEmpty() ? createValidationResponse(errors) : Response.ok(new GHGadget(preferences)).cacheControl(com.pyxis.greenhopper.gadget.CacheControl.NO_CACHE).build();

As part of this issue, I suggest you review all other responses which contain dynamic data and make sure they have the required NO-CACHE header.
If no caching behavior is specified inside JIRA the response will not have any caching information, but when going through the gadget proxy it will add a default cache timeout of 2 hours. Which means these gadgets will stop to work in external gadget containers.