Search pattern: switching between algorithms is inaccurate

Scenario:

1. Load sample/Genbank/sars.gb
2. Open Search in Sequence option tab
3. Search algorithm=Exact by default
4. Insert "Z"
   Expected: Field is red
5. Select algorithm=Substitute, check Search with ambiquous bases checkbox
   Expected: Field is white
6. Select Search algorithm=Exact
   Expected: Field is red
7. Select Search algorithm=Substitute again
   Expected: Field is white, Search with ambiquous bases checked
   Actual: Field is red, Search with ambiquous bases checked
8. Uncheck Search with ambiquous bases and check it again
   Actual: OK, field is white