In this case, the control is populated with business objects. The AutoCompleteDisplayMember property of the control point to a property of this object. This property can have a similar value to more than one item from the source collection. When we try to select a specific item using the Text property, the control will select the first occurrence of the value that is found in the collection. This behavior can be improved to allow to select specific item from the collection with duplicate values.

Please run the sample project and enter some tokens. Then, hit Backspace and the following error occurs:

System.ArgumentOutOfRangeException: startIndex cannot be larger than length of string.
Parameter name: startIndex
   at System.String.Substring(Int32 startIndex, Int32 length)
   at Telerik.WinControls.UI.TextBoxViewElement.ReplaceTextBlock(ITextBlock targetBlock, Int32 startCharPosition, Int32 endCharPosition, String text)
   at Telerik.WinControls.UI.TextBoxViewElement.ReplaceTextRange(ITextBlock targetBlock, Int32 startCharPosition, Int32 endCharPosition, String text)
   at Telerik.WinControls.UI.AutoCompleteBoxViewElement.ReplaceTextRange(ITextBlock targetBlock, Int32 startCharPosition, Int32 endCharPosition, String text)
   at Telerik.WinControls.UI.TextBoxViewElement.ReplaceOverride(TextPosition startPosition, TextPosition endPosition, String text)
   at Telerik.WinControls.UI.AutoCompleteBoxViewElement.ReplaceOverride(TextPosition startPosition, TextPosition endPosition, String text)
   at Telerik.WinControls.UI.TextBoxViewElement.Replace(TextPosition startPosition, TextPosition endPosition, String text)
   at Telerik.WinControls.UI.RadTextBoxControlElement.Delete(Boolean nextCharacter, Boolean isControlPressed)
   at Telerik.WinControls.UI.TextBoxInputHandler.ProcessDelete(Boolean moveNext, Boolean isControlPressed)
   at Telerik.WinControls.UI.TextBoxInputHandler.ProcessKeyDown(KeyEventArgs e)
   at Telerik.WinControls.UI.RadTextBoxControlElement.OnKeyDown(KeyEventArgs e)
   at Telerik.WinControls.RadItem.DoKeyDown(KeyEventArgs e)
   at Telerik.WinControls.RadItem.RaiseBubbleEvent(RadElement sender, RoutedEventArgs args)
   at Telerik.WinControls.RadElement.RaiseRoutedEvent(RadElement sender, RoutedEventArgs args)
   at Telerik.WinControls.RadItem.RaiseKeyDown(KeyEventArgs e)
   at Telerik.WinControls.ComponentInputBehavior.OnKeyDown(KeyEventArgs e)
   at Telerik.WinControls.RadControl.OnKeyDown(KeyEventArgs e)
   at System.Windows.Forms.Control.ProcessKeyEventArgs(Message& m)
   at System.Windows.Forms.Control.ProcessKeyMessage(Message& m)
   at System.Windows.Forms.Control.WmKeyChar(Message& m)
   at System.Windows.Forms.Control.WndProc(Message& m)
   at System.Windows.Forms.ScrollableControl.WndProc(Message& m)
   at Telerik.WinControls.RadControl.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.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)