I'm adding a few similarly-named tags to a task; having added the first, I then start typing for the second tag but have to type more than I would need to limit the field to five tags that include the one I now want. For the third it involves still more typing.
What I'd like to happen: When writing into a multi-input box (in this case, tags for a task), the type-ahead suggested results filters out ones present in the box so I have fewer from which to choose more quickly.
Note that this is also present even more irritatingly (but in a less frequent workflow) when trying to use Maniphest's advanced search for e.g. tasks closed in the past month but not in either of the two relevant sprints, as the triple-meta-tag suggestions (X, In any X, Not in X) mean the sixth option (not Y) isn't present; though we can extend the list to e.g. ten, it just means that the meta-tags for the fourth sprint are absent instead.