Sources found at http://dogfeathers.com/mark/java7issue.html

Index: tigervnc.new/java/src/com/tigervnc/vncviewer/VncViewer.java
===================================================================
--- tigervnc.new.orig/java/src/com/tigervnc/vncviewer/VncViewer.java	2012-08-21 09:05:04.000000000 +0200
+++ tigervnc.new/java/src/com/tigervnc/vncviewer/VncViewer.java	2012-08-21 09:10:27.000000000 +0200
@@ -110,6 +110,28 @@
 
   public void init() {
 
+    // fix focus traversal  
+    Container topParent = null;
+    Container parent = this;
+    // The natural thing would be to call getParent() until it returns
+    // null, but then you would be looping for a long time, since
+    // PluginEmbeddedFrame's getParent() returns itself.
+    for (int k=0; k < 10; k++) {
+      topParent = parent;
+      parent = parent.getParent();
+      if (parent == null) break;
+    }
+
+    // If topParent isn't a KeyEventDispatcher then we must be in some
+    // Plugin version that doesn't need the workaround.
+    try {
+      KeyEventDispatcher ked = (KeyEventDispatcher)topParent;
+      KeyboardFocusManager kfm = KeyboardFocusManager.getCurrentKeyboardFocusManager();
+      // You have to remove it twice, otherwise the problem isn't fixed
+      kfm.removeKeyEventDispatcher(ked);
+      kfm.removeKeyEventDispatcher(ked);
+    } catch (ClassCastException e) {}
+
     readParameters();
 
     refApplet = this;