Steps to reproduce:
1. Go to Dashboard
2. Open 'Problems' widget create form and add Problem tags:
-) Operator -> Contains
-) Value -> a
3. Apply changes and save the dashboard
4. Open edit form for the newly created widget
5. Change Problem tag to:
-) Operator -> Exists
6. Apply changes and save the dashboard
7. Open the edit form again and change the tag operator to 'Does not contain' or any other that may contain value.

Result: Previously saved value still exists and is displayed for operators that contain a value field. Please see the video attachment.


Expected: I suppose that the value should be updated to ' ' after step #6 because tags with operator 'Exists' doesn't contain the value field.