Left layer does not allow contextual menu to pop. Right one does. When a contextual menu is shown and without hiding it you rightclick on the layer to the left, the contextual menu shows anyway in NS4. This behaviour is to be studied but it may not be solvable.

    	myListener = new EventListener()
    		myListener.onrtmouseup=function(e) {
    			e.cancelBrowserEvent()
    		}
    		myListener.onrtmousedown=function(e) {
    			e.cancelBrowserEvent()
    		}

Notice that this can easily be made into an extension with DynObject.prototype.allowContextuals(true/false) that would add/remove the above listener to the layer calling the method. This is some easy homework for those who want to starting getting their hands dirty.