I also noticed that the blur and focus events were not correctly triggered; 
for example, suppose you have the opened popup of the multiselect A, and you click on multiselect B: in the DropDownTrait class, the _afterDropdownClose() method triggers the focus on multiselect A before the focus event triggered by the user click action is executed on multiselect B.
This is not totally correct because a focus and a blur events are unnecessarily executed for multiselect A;