CMS UI entity filtering for a type multi-select field is not working.

[pnikolov]

The fix is amending the cms/views/_shared/entities/types/multiselect/filter.html.tpl: From this:

<select name="filtering[{$field}]" id="filter-attribute-{$field}[]" ...
...

to this:

<select name="filtering[{$field}][]" id="filter-attribute-{$field}" ...