Problem: Can't drop a dropdown list or combo box on toolbar
When dragging the Edit Task control from Customization Dialog and dropping it on the toolbar, the Edit Task control does not appear on the toolbar.
The Edit Task control is already on the Editor toolbar. Currently, ArcGIS applications limit a single instance of any tool control per application instance. If the control already exists elsewhere on that bar or another bar, the drop will not work.
Solution or Workaround
Use the existing control.