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Weird behavior updating a dropdown menu’s contents dynamically

I tried to follow these steps, which worked great until I wanted to enable selecting multiple second level values.

In the solution from link above, if you replace dcc.RadioItems(id='cities-dropdown'), with dcc.Checklist(id='cities-dropdown'),you get some weird behavior:

The first meny item seem to hang, and is separated into characters. Is there a simple fix to this?