[Service,WebView] Security exception in Service.cancel and URLLoaderThreadFactory when running sandboxed applet

The following exception occurs when trying to load an URL in WebView in Java 8u25 in a Sandboxed Applet.

The URL is this (but i do not think it matters which URL it is):
http://chat.knuddels.de:2720/apps/api/loader.html?client=Applet

java.security.AccessControlException: access denied ("java.lang.RuntimePermission" "modifyThreadGroup")
at java.security.AccessControlContext.checkPermission(Unknown Source)
at java.security.AccessController.checkPermission(Unknown Source)
at java.lang.SecurityManager.checkPermission(Unknown Source)
at sun.plugin2.applet.SecurityManagerHelper.checkAccessHelper(Unknown Source)
at sun.plugin2.applet.AWTAppletSecurityManager.checkAccess(Unknown Source)
at java.lang.ThreadGroup.checkAccess(Unknown Source)
at java.lang.Thread.init(Unknown Source)
at java.lang.Thread.init(Unknown Source)
at java.lang.Thread.<init>(Unknown Source)
at com.sun.webkit.network.NetworkContext$URLLoaderThreadFactory.newThread(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.<init>(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor.addWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor.execute(Unknown Source)
at java.util.concurrent.AbstractExecutorService.submit(Unknown Source)
at com.sun.webkit.network.NetworkContext.fwkLoad(Unknown Source)
at com.sun.webkit.network.URLLoader.twkDidReceiveData(Native Method)
at com.sun.webkit.network.URLLoader.notifyDidReceiveData(Unknown Source)
at com.sun.webkit.network.URLLoader.lambda$didReceiveData$91(Unknown Source)
at com.sun.webkit.network.URLLoader$$Lambda$157/157794.run(Unknown Source)
at com.sun.javafx.application.PlatformImpl.lambda$null$164(Unknown Source)
at com.sun.javafx.application.PlatformImpl$$Lambda$67/15013748.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.application.PlatformImpl.lambda$runLater$165(Unknown Source)
at com.sun.javafx.application.PlatformImpl$$Lambda$66/31250559.run(Unknown Source)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(Unknown Source)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$141(Unknown Source)
at com.sun.glass.ui.win.WinApplication$$Lambda$54/27601048.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)

This is a blocker for our next release, as we rely heavily on the WebView technology for our newest project.