[BUG] Dropdown "multi" argument not working in latest release

[GoldwinXS]

Describe your context

• python 3.9

• latest release

• if frontend related, tell us your Browser, Version and OS
  chrome, safari, probably all

Describe the bug

multi argument for Dropdown is not working. Adding that argument results in only one value in the list, and the text for the dropdown does not update. In the exact same situation (literally just commenting out multi=True) gives a dropdown with the correct behaviour.

I can add my code if you'd like, but it absolutely accounts for multi dropdown behaviour.

Expected behavior (behavioUr c'mon you're a canadian company :P)

I expect that the "multi" argument from dcc.Dropdown behaves like previous versions of dash, where value yields a list of variable length.

Screenshots

I've downgraded dash to 1.21.0 and that's fixed my issue. I don't really feel like recreating it and ultimately going through more effort here, as it has already wasted a lot of my time...

[BWalzer]

I'm running into the same issue. I think commas in the options are causing this. Here's an example where the first dropdown works, but the second doesn't.

app.layout = html.Div(
    [
        # This dropdown works as expected: Montreal, San Francisco, and New York City
        #   are all options to choose, with Montreal and San Francisco selected when loaded.
        dcc.Dropdown(
            ['New York City', 'Montreal', 'San Francisco'],
            ['Montreal', 'San Francisco'],
            multi=True
        ),

        # This dropdown DOES NOT work as expected: Montreal, San Francisco, and New York City
        #   are all options to choose, but nothing is selected when loaded.
        #   Trying to select new options does not update the dropdown menu.
        dcc.Dropdown(
            ['New York City, NY', 'Montreal, QC', 'San Francisco, CA'],
            ['Montreal, QC', 'San Francisco, CA'],
            multi=True
        )
    ]
)

python 3.6.8
dash version 2.1.0

[nickmelnikov82]

Duplicate of #1908

[T4rk1n]

Fixed by #1970