Custom templates stopped working

So, after all, it was a wordpress bug apparently…

The problem is I was registering the following year taxonomy:

register_taxonomy('year', array('project'), array(
        'hierarchical'      => true,
        'labels'            => array('name' => 'Anos', 'singular_name' => 'Ano'),
        'show_ui'           => true,
        'public' => false
));

And it seems year is a reserved word for WP’s rewriting rules, and it must have gotten confused because of this. I simply renamed the taxonomy and updated the permalinks and everything started working again:

register_taxonomy('project-year', array('project'), array(
        'hierarchical'      => true,
        'labels'            => array('name' => 'Anos', 'singular_name' => 'Ano'),
        'show_ui'           => true,
        'public' => false
));

I believe there must be other reserved names and the same problem might happen to register_post_type function too.