[Vuejs]-Function returning true despite promise evaluating to false

So @Axnyff found this semantic-ui beug report, which led me to the solution:

onApprove() {
    that.$validator.validate().then((result) => {
        if (result) {
            $.ajax({
                ...
                },
                complete() {
                    $('#modify_user_modal').modal('hide'); // Manually hide.
                },
            });
        }
    });
    return false; // Modal never closes.
},