SUGGESTED FIX

--- a/src/windows/classes/sun/awt/windows/WInputMethod.java     Tue Aug 26 16:31
:13 2008 +0400
+++ b/src/windows/classes/sun/awt/windows/WInputMethod.java     Tue Aug 26 20:53
:28 2008 +0400
@@ -548,11 +548,15 @@ public class WInputMethod extends InputM

     public void inquireCandidatePosition()
     {
+        Component source = getClientComponent();
+        if (source == null) {
+            return;
+        }
         // This call should return immediately just to cause
         // InputMethodRequests.getTextLocation be called within
         // AWT Event thread.  Otherwise, a potential deadlock
         // could happen.
-        java.awt.EventQueue.invokeLater(new Runnable() {
+        Runnable r = new Runnable() {
             public void run() {
                 int x = 0;
                 int y = 0;
@@ -573,7 +577,9 @@ public class WInputMethod extends InputM

                 openCandidateWindow(awtFocussedComponentPeer, x, y);
             }
-        });
+        };
+        WToolkit.postEvent(WToolkit.targetToAppContext(source),
+                           new InvocationEvent(source, r));
     }

     // java.awt.Toolkit#getNativeContainer() is not available
                                     

EVALUATION

I couldn't reproduce the problem on my WinXP desktop so far... After a quick look to the code I have found a single suspicious place in WInputMethod.java:

    public void inquireCandidatePosition()
    {
        ...
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                ...
            }
        });
    }

This code is obviously must be rewritten because EventQueue methods know nothing about AppContexts, and the Runnable may be executed on wrong EDT.
                                     

EVALUATION

The reason for this behavior is that in some cases input events are posted to several AWT threads at once, and eventually all these threads call to Swing attempting to do re-layout at the same time. Swing is not thread-safe, so it messes up its internal structures which leads to spurious NPEs, deadlocks etc. preventing an applet from responding.

Re-assigning to the AWT team.