My own macro in volt file not rendering correctly

In fact even I understand what's going on. I created some "components" using macros in the template volt model. But I do not understand what the problem is. Any macro that I do is like that. Here's an example:

{%- macro foo(bar='') %}
    <h1>{{ bar }}</h1>
{%- endmacro %}

then:

{{ partial('correct/path/to/macro')}}
{{ foo('My text here') }}

This render: <h1>M</h1>, the right was to be: <h1>My text here</h1>

Any idea what's going on?

My system:

Linux Mint Rafaela 17.2 Cinnamon / Apache 2 / PHP 5.5.9 / Phalcon 2.0.11

EDIT1: Thinking that the problem could be in my project, I created a new simple and create a simple macro the same problem appears.