An ArgumentOutOfRangeException is thrown when the Separator property is set to a string that contains alpha-numeric/numeric "not required" mask tokens, and the clear button is pressed. The control works with a custom RadMaskedTextInput control to parse different date and time patterns for the start and end dates, which replaces the mask tokens with a placeholder, resulting in the exception when updating the Value property of the RadMaskedTextInput when the value is cleared.