fixed small logical error with startDrag()

src/DragAndDrop.js

@@ -93,7 +93,11 @@
             ap = this.getAbsolutePosition(), 
             animNode = layer || this;
                 
-        if(pos && !dd.node) {
+        if(pos) {
+            if (dd.node) {
+                dd.node.stopDrag(); 
+            }
+          
             dd.node = this;
             dd.offset.x = pos.x - ap.x;
             dd.offset.y = pos.y - ap.y;

src/Stage.js

@@ -425,7 +425,7 @@
             }
 
             //init stage drag and drop
-            if(this.isDraggable()) {
+            if(this.isDraggable() && !dd.node) {
                 this.startDrag(evt);
             }
         },