Validating a custom field (set to required) showing duplicate values

Issue Summary

Validation of a custom field (That is marked as Required) shows a duplicate value that has "not available" displayed on the workflow transition screen in case the validation fails.

Steps to Reproduce

1. Create a custom field "Checkboxes (Choose multi values using checkboxes)". Add one value to the checkbox list.  
2. Set the custom field as required. And add it to any of the transition screens.
3. As it is a required field, the checkbox has to be checked while creating the issue.
4. Later while performing transition this field appears on the screen with the option checked.
5. Uncheck the field and proceed to submit.
6. The form would not be submitted (which is expected) but there is a duplicate value displayed on the screen of the checkbox with "not available" displayed at the end like below.

      AffirmationRequired

• I Affirm this to be a valid request
• I Affirm this to be a valid request (not available)

Expected Results

The duplicate value or incorrect display should not appear on the screen. 

Actual Results

A duplicate value with "not available" at the end is displayed on the screen.

Workaround

This doesn't cause any functional impact. Users can still proceed to select one of the fields and proceed to form submission. But it is an incorrect screen display.