Setting Dropdown value to None does not appear to work when calling Event Listener

I have a two Dropdown components within a block. The first Dropdown loads a list of choices by default. The second Dropdown loads choices based on the first Dropdown selection (dropdown1.input…). When I change Dropdown 1, I want the default value of Dropdown 2 to be None. However, it won’t always reset to None. Sometimes it selects one of the values of the new choices. Thoughts?