Steps to reproduce:

1. Go to edit/create a Discovery rule's filters.
2. Simply click on Add several times.
3. Observe labels are in order - A, B, C...
4. Note the last row's letter (e.g. C).
5. Click Remove on the last row.
6. Click Add.
7. Observe the letter is advanced to next in the alphabet (e.g. D), instead of the one in step 4 (C).
8. Cycling remove-add on the last row further advances the letter.
9. Save the filter.
10. Observe labels are "re-lettered" to order.

Result:

Expected:
The subsequent letter by alphabet is re-used (C instead of G in the screenshot), matches state when saved.

Likely same issue in override filters.