order_by attribute on with_scope not working?

Neither on the engine nor on wagon, this ordering seems to work:

{% with_scope start.gt: now, order_by: 'start.asc' %}
    {% assign future_events = contents.events %}
{% endwith_scope %}

The order as defined in events.yml is start.desc, which is also the order I get regardless of the order defined in the with_scope tag.