Index: generic/tkEvent.c
==================================================================
--- generic/tkEvent.c
+++ generic/tkEvent.c
@@ -1206,10 +1206,18 @@
     unsigned long mask;
     InProgress ip;
     Tcl_Interp *interp = NULL;
     ThreadSpecificData *tsdPtr =
 	    Tcl_GetThreadData(&dataKey, sizeof(ThreadSpecificData));
+
+#if !defined(MAC_OSX_TK) && !defined(_WIN32)
+    if (((eventPtr->type == ButtonPress) || (eventPtr->type == ButtonRelease))
+	    && ((eventPtr->xbutton.button - 6) < 2)) {
+	eventPtr->xbutton.button -= 2;
+	eventPtr->xbutton.state |= ShiftMask;
+    }
+#endif
 
     UpdateButtonEventState(eventPtr);
 
     /*
      * If the generic handler processed this event we are done and can return.