Can not call function without parameters

It seems that I cannot call a function without parameter. I have a very simple dialog ("what time is it?", "it is 12 o'clock") that does not require a parameter. When I create a block like:

```
{% block %}
{% client %}(what time is it){% endclient %}
{% response %}{% call time %}{% endresponse %}
{% endblock %}
```
The response is simply "time" instead of the result of calling time. When I add a dummy variable and use `{% call time:0 %}` it works well.