Unique elements for dropdown works, but not for multi dropdown

I have a data type that contains State, County, City, and Zip.

In my form, I can set the dropdown Choice style, Type of choices, and Choice source to not show duplicate counties based on the selected State from a separate dropdown.

However, when I set a Multi Dropdown with the same exact setting, the unique element’s county is not working and showing duplicate counties in the multi-select dropdown. Is there an additional setting I’m missing that is required on a multi-select dropdown vs the standard single select dropdown? Thank you.