Only respond to drag-drop of tabs in tab bar.

src/packages/tabs/lib/tab-bar-view.coffee

@@ -81,6 +81,8 @@ class TabBarView extends View
       event.preventDefault()
       return
 
+    event.originalEvent.dataTransfer.setData 'atom-event', true
+
     el = $(event.target).closest('.sortable')
     el.addClass 'is-dragging'
     event.originalEvent.dataTransfer.setData 'sortable-index', el.index()
@@ -93,6 +95,11 @@ class TabBarView extends View
     @find(".is-dragging").removeClass 'is-dragging'
 
   onDragOver: (event) =>
+    unless event.originalEvent.dataTransfer.getData('atom-event') == true
+      event.preventDefault()
+      event.stopPropagation()
+      return
+
     event.preventDefault()
     currentDropTargetIndex = @find(".is-drop-target").index()
     newDropTargetIndex = @getDropTargetIndex(event)
@@ -107,6 +114,11 @@ class TabBarView extends View
 
 
   onDrop: (event) =>
+    unless event.originalEvent.dataTransfer.getData('atom-event') == true
+      event.preventDefault()
+      event.stopPropagation()
+      return
+
     event.stopPropagation()
     @children('.is-drop-target').removeClass 'is-drop-target'
     @children('.drop-target-is-after').removeClass 'drop-target-is-after'

src/packages/tabs/spec/tabs-spec.coffee

@@ -278,3 +278,19 @@ describe "TabBarView", ->
         expect(pane2.getItems()).toEqual [item2b, item1]
         expect(pane2.activeItem).toBe item1
         expect(pane2.focus).toHaveBeenCalled()
+
+    describe 'when a non-tab is dragged to pane', ->
+      it 'has no effect', ->
+        expect(tabBar.getTabs().map (tab) -> tab.text()).toEqual ["Item 1", "sample.js", "Item 2"]
+        expect(pane.getItems()).toEqual [item1, editSession1, item2]
+        expect(pane.activeItem).toBe item2
+        spyOn(pane, 'focus')
+
+        [dragStartEvent, dropEvent] = buildDragEvents(tabBar.tabAtIndex(0), tabBar.tabAtIndex(0))
+        tabBar.onDrop(dropEvent)
+
+        expect(tabBar.getTabs().map (tab) -> tab.text()).toEqual ["Item 1", "sample.js", "Item 2"]
+        expect(pane.getItems()).toEqual [item1, editSession1, item2]
+        expect(pane.activeItem).toBe item2
+        expect(pane.focus).not.toHaveBeenCalled()
+