Ok I dug into the code myself and I found the problem:
First on line 83 of /flexform/archive.php the $author variable is being set with an object.
<?php $author = get_userdata( get_query_var('author') ); ?>
Then on lines 378-380 of /breadcrumb_navxt/breadcrumb_navxt_class.php the global reference to $author is being accessed. $author should be int, however it is now an object set from the archive page in flexform, thus the return value will always be 1 (user_id #1).
global $author;
//Get the Author name, note it is an object
$curauth = (isset($_GET['author_name'])) ? get_userdatabylogin($author_name) : get_userdata(intval($author));
I have disabled all plugins and changed my theme to TwentyTwelve and the $author variable is global and is correctly set to the author ID. I am not sure who’s bug this is (flexform, wp, or breadcrumb-navxt) because according to the WP codex, $author is not listed as a global (only $authordata). However breadcrumb-navxt is obviously expecting a global $author.
Hope this helps.
~Jason