I don't know if this is the correct place to report bugfixes for the p2theme.
The function p2_get_discussion_links uses the author name for building the link to the posts of a commenting author, instead of the login name.
template-tags.php line 113 should be changed from:
$user_info = get_userdata($comment->user_id);
$content .= 'user_login ) ) . '">' . esc_attr( $comment->comment_author ) . '';