There are 2 problems.

Using "MultiValueDeselectBox" control by Document Value, after you have saved the document, the multivalue field  on the notes document isn't multivalue, but it's a string with comma as separator.

Another problem occurs when after you have saved document and you try to remove value from multivalue field by x icon near value, it seems that the update is success but if you save the document again, the removed value re appear. Could you help me ? am I making a mistake?

Thanks a lot for your attention.