Drop-down area is not repositioned if still open when multi-select area changes size (e.g. closeOnSelect=false) #4377

Prerequisites

• I have searched for similar issues in both open and closed tickets and cannot find a duplicate
• The issue still exists against the latest master branch of Select2 (4.0.2) - Unknown
• This is not a usage question
• I have attempted to find the simplest possible steos to reproduce the issue

Steps to reproduce the issue

1. Enable tagging (tags:true), and do not close the drop-down on select/deselect actions (closeOnSelect:false).
2. Add and remove (select/deselect) choices to make the tags area change height.
3. When the tags area changes height, the drop-down element is not repositioned accordingly.

Expected behavior and actual behavior

The drop-down element should be repositioned when the tags area changes size.

Here is a tagged selection area with a few tags already selected:

This is what happens when one or more tags are selected and the tags area changes size (in this case, gets taller):

The newly selected choices have been added to the tags area, but their tags are hidden behind the drop-down element. The drop-down element is not repositioned (in this case, lowered) to expose the added tags.

Work-Around

I used a work-around, catching the "change" event and forcing a resize of the drop-down element:

// Force drop-down list to resize upon select/unselect
select2Elem.on("change",
    function(evt) {
        select2Elem.resize();
    }
);

Environment

Any browser.
Any O/S.

• Select2 version: 4.0.2

External Links

The same bug was reported on StackOverflow at: http://stackoverflow.com/questions/37198185