Manually typed values do not get saved if they're not checkboxed

Current behavior: Some of our users are typing the values directly in the textbox, instead of selecting the values from the list of checkboxed values. When the work item is saved, those typed values are lost if they’re not also selected with the checkboxes.   Desired behavior: I type [value1] in the text box. Upon saving, the custom control checks if [value1] is a valid SUGGESTEDVALUE. If it is a valid value, then it saves it even if it’s not checkboxed.