For some reason, the 'keydown' event is being unbound when the suggestions popup appears, so the function is never firing. However, it seems like they shouldn't be listening to keydown anyway because they only care about when the enter key is pressed and that event is already available on the input as the 'enter' event (from OO.ui.TextInputWidget).
With love from the Wikia development team.
Version: unspecified
Severity: minor