Error when SyntaxEditor receives focus

I am getting the following error when the SyntaxEditor control receives focus. It doesn't happen that often and it usually happens only when the control receives focus after being hidden:

Top Level Exception
Type: System.ArgumentException
Message: The offset '0' added to the length '1' must be less than or
equal to the count of characters in the document.
Source: ActiproSoftware.SyntaxEditor
Stack Trace: at ActiproSoftware.SyntaxEditor.Document.?(Int32 , Int32 )
at ActiproSoftware.SyntaxEditor.Document.GetSubstring(Int32 offset,
Int32 length)
at ActiproSoftware.SyntaxEditor.EditorView.get_SelectedText()
at ?.?(EditorView )
at ?.OnMouseMove(UIComponentMouseEventArgs e)
at
ActiproSoftware.WinUICore.UISelectionService.?(UIComponentMouseEventArgs
)
at ActiproSoftware.WinUICore.UIObject.?(UIComponentMouseEventArgs )
at
ActiproSoftware.WinUICore.UIObject.OnMouseMove(UIComponentMouseEventArgs
e)
at
ActiproSoftware.WinUICore.UIObject.ActiproSoftware.WinUICore.IUIComponen
t.RaiseMouseMoveEvent(UIComponentMouseEventArgs e)
at ActiproSoftware.WinUICore.UIControl.OnMouseMove(MouseEventArgs e)
at System.Windows.Forms.Control.WmMouseMove(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.UserControl.WndProc(Message& m)
at System.Windows.Forms.ControlNativeWindow.OnMessage(Message& m)
at System.Windows.Forms.ControlNativeWindow.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg,
IntPtr wparam, IntPtr lparam)

Thanks