Create two picklists on the case object. Make PicklistOne control PicklistTwo.
- Add an option to PicklistOne of "A"
- Add an option to PicklistTwo of "B C" Note that there are two spaces between B and C
- Open the visualforce page and feed an id to it like so /apex/TestVFPage?id=500S0000xxxx
- Select "A" in PicklistOne.
- Select "B C" in PicklistTwo.
- Click "Click Me"
- The value in PicklistTwo is cleared.