NullReferenceException when disposing and control has focus

[cvogt61457]

There is a NullReferenceException when disposing and control has focus.

When disposing, the FieldControls and LabelControls are disposed.
The base.Dispose(disposing) is then called.

A NullReferenceException is thrown from inside the base.Dispose().
Unhandled Exception: System.NullReferenceException: Object reference not set to an instance of an object.
at IPAddressControlLib.IPAddressControl.get_Focused()
at IPAddressControlLib.IPAddressControl.OnLostFocus(EventArgs e)
at System.Windows.Forms.Control.WmKillFocus(Message& m)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.ScrollableControl.WndProc(Message& m)
at System.Windows.Forms.ContainerControl.WndProc(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

It appears that get_Focused() accesses the null _fieldControls causing the exception.