Error: Assertion failed: Input listener already registered on this Node
at window.assertions.assertFunction (http://localhost:8080/assert/js/assert.js:21:13)
at PusherNode.addInputListener (http://localhost:8080/scenery/js/nodes/Node.js?bust=1500513204604:1632:17)
at Array. (http://localhost:8080/forces-and-motion-basics/js/motion/view/PusherNode.js?bust=1500513204604:354:14)
at Emitter.emit2 (http://localhost:8080/axon/js/Emitter.js?bust=1500513204604:147:49)
at Property._notifyObservers (http://localhost:8080/axon/js/Property.js?bust=1500513204604:207:29)
at Property._setAndNotifyObservers (http://localhost:8080/axon/js/Property.js?bust=1500513204604:196:14)
at Property.set (http://localhost:8080/axon/js/Property.js?bust=1500513204604:140:16)
at ObservableArray.push (http://localhost:8080/axon/js/ObservableArray.js?bust=1500513204604:228:27)
at ObservableArray.add (http://localhost:8080/axon/js/ObservableArray.js?bust=1500513204604:173:12)
at moveToStack (http://localhost:8080/forces-and-motion-basics/js/motion/view/ItemNode.js?bust=1500513204604:93:19)
now an assertion failure from https://github.com/phetsims/scenery/issues/651.