Inconsistent autocompletion behavior for constructors

When triggering autocompletion on a constructor, when one continues typing, the selected/relevant proposal is lost, as some leading characters seem to be missing from the selection.

Additionally, in some circumstances, eg. after triggering autocomplete then deleting the previous character, the injected text is missing the leading characters (one or many).

See https://www.screencast.com/t/17vjLA8vC0hq