"Field has been modified Validator" does not work for Text Field (multi-line) if it has default value

Summary

When a validator Field has been modified Validator is set on a transition for a "Text Field (multi-line)" field, the transition goes through even if it's not being modified during the transition.

Steps to reproduce

1. Create a custom field with type Text Field (multi-line)
2. Set default value of the custom field.
3. Add Field has been modified Validator validator (with an error message) to a transition to check if the field's value is being updated during transition
4. Add a screen, that contains the field
5. Create an issue and add a value to the custom field in edit/view issue screen
6. Transition the issue using the transition in which the validator is set. Do not update/modify the field's value during transition

Expected Result

Issue could not be transitioned as the field's value is not being modified during the transition

Actual Result

The transition goes through even if the field's value is not updated

Note

If the field is empty and it has never a value the validator works fine and the validator error message appears during the transition. But if the field has a value, or it has value previously and is empty now, the validator does not work.

Workaround

Use the Value Field condition: "The field <Field Name> will have to be not equal to value 'NULL'. Compared as String."
(change the Field as per your site)