CiviEvent 4.7* Wordpress - calculated fees with default values doubled w/WP Plugin
It turned out that the problem was due to a Wordpress plugin I set up called Inactive Logout (https://wordpress.org/plugins/inactive-logout/) caused the problem. Once I deactivated the plugin all worked well.
 Moral of the story: beware the smiling WP plugin, the javascript that bites, the session vars that snatch, beware the easy download and shun the frumious extension.
 On a serious note I think the plugin doubled the logged-in users but have to investigate.

It turned out the problem was caused by a call to wp_footer in src/inactive-logout-functions.php line 16, commenting-out that line fixed the problem and the inactive logout still works. wp-footer appends data to the /body tag