Don't end drag when parent removed

js/id/behavior/drag.js

@@ -24,7 +24,7 @@ iD.behavior.drag = function() {
         origin = null,
         selector = '',
         filter = null,
-        event_, target;
+        event_, target, surface;
 
     event.of = function(thiz, argumentz) {
       return function(e1) {
@@ -62,14 +62,13 @@ iD.behavior.drag = function() {
         if (touchId === null) d3_eventCancel();
 
         function point() {
-            var p = target.parentNode;
+            var p = target.parentNode || surface;
             return touchId !== null ? d3.touches(p).filter(function(p) {
                 return p.identifier === touchId;
             })[0] : d3.mouse(p);
         }
 
         function dragmove() {
-            if (!target.parentNode) return dragend();
 
             var p = point(),
                 dx = p[0] - origin_[0],
@@ -170,5 +169,11 @@ iD.behavior.drag = function() {
         return drag;
     };
 
+    drag.surface = function() {
+        if (!arguments.length) return surface;
+        surface = arguments[0];
+        return drag;
+    };
+
     return d3.rebind(drag, event, "on");
 };

js/id/behavior/drag_node.js

@@ -148,6 +148,7 @@ iD.behavior.DragNode = function(context) {
 
     var behavior = iD.behavior.drag()
         .delegate("g.node, g.point, g.midpoint")
+        .surface(context.surface().node())
         .origin(origin)
         .on('start', start)
         .on('move', move)