When using the JNLP DownloadService API with the default DownloadServiceListener, the DownloadServiceListener will throw an exception on the second call to loadResource(), because when closing the window the first time, the window is put in canceled state, causing the second usage to immeadiatly think the user has canceled the download.
This was caused by the GUI redesign in 1.6.0 in DownloadWindow.java, but can be most easily fixed in DownloadServiceImpl.java by reseting the canceled state whenever creating a new ProgressHelper object.
also related problem using DownloadService to download jars not in jnlp file - AppPolicy.java assumes jarDesc has parent and throws NPE, jars not from jnlp file should just get sandbox permissions.