Possible to add same term twice when autocomplete is off

Problem/Motivation

When using autocomplete in the Select2 widget, it filters out already selected terms and doesn't allow user to add it a second time. The same doesn't seem to work when autocomplete is disabled.

Also it seems like when you add the same term a second time, it removes both terms.

Autocomplete is nice for long lists fo select values but it seems like it works in a wrong way when there are limited number of values and autocomplete is not needed.

Steps to reproduce

1. Create a field with a taxonomy reference field.
2. Enable Select2 and disable autocomplete.
3. Select a term.

Currently it allows you to select the same term twice. And it also removes both terms when the second term is selected.

The expected result would be that already selected terms would be removed from the list.