strip off extra bits set by Xorg in event state

ChangeLog

@@ -1,6 +1,8 @@
  (Format: Year/Month/Day)
 Changes for 1.0.0:
 *07/06/28:
+   * Strip off additional bits in event state set by Xorg, bug #1736252 (Mark)
+     FbTk/KeyUtil.hh
    * Added some missing Open Office entries and window managers, plus some other
      minor changes in fluxbox-generate_menu
      fluxbox-generate_menu.in

src/FbTk/KeyUtil.hh

@@ -69,8 +69,9 @@ public:
         @return the cleaned state number
     */
     unsigned int cleanMods(unsigned int mods) {
-        //remove numlock, capslock and scrolllock
-         return mods & ~(capslock() | numlock() | scrolllock());
+        // remove numlock, capslock, and scrolllock
+        // and anything beyond Button5Mask
+        return mods & ~(capslock() | numlock() | scrolllock()) & ((1<<13) - 1);
     }
 
     /**