Steps to reproduce the issue

Try to create a custom filed and select a category different from "All":

"All" remain as a text after the category selected

Expected result

OR

OR

Actual result

Additional comments

I think the problem is that "All" option have no value

<joomla-field-fancy-select  search-placeholder="Type or Select a Category" ><select id="jform_assigned_cat_ids" name="jform[assigned_cat_ids][]" multiple>
	<option value="">All</option>
	<option value="-1" selected="selected">None</option>
	<option value="2">Uncategorised</option>
	<option value="8">Blog</option>
	<option value="9">Help</option>
</select>

Also, there shouldn't be able to select a category (or "All") and "none" at the same time: