Personalised results bulk add doesn't replace domain preferences despite stating it does.

I bulk added this list of over 240 domains to my personalised results as a block list.
Tried to replace the list by bulk adding a much shorter list containing only two domains.
The huge list of domains still persists in my personalised results settings as a block list.

I expected the list to be replaced with the shorter list, as the page states "Existing domain preferences will be replaced with the new preference."