MultiformeIngegno on "get_avatar retrieves avatar passing from i0.wp.com"

Here's my function:

<?php echo get_avatar( $comment, $size = '35', $default = 'http://bombacarta.com/wp-content/themes/raymond-31/images/default_avatar.png' ); ?>

The problem is that instead of my local URL the output is:
http://i0.wp.com/bombacarta.com/wp-content/themes/raymond-31/images/default_avatar.png

I have all plugins DISABLED!!! What the hell is happening? :o