mw.widgets.UsersMultiselectWidget.prototype.updateHiddenInput = function () {
if ( 'hiddenInput' in this ) {
this.hiddenInput.val( this.getSelectedUsernames().join( '\n' ) );
+ // Hidden inputs do not trigger onChange.
+ // @see https://developer.mozilla.org/en-US/docs/Web/HTML/Element/input/hidden
+ this.hiddenInput.trigger( 'change' );
}
};