Ajax HTTP error occurred + htmlspecialchars()

I have the Devel error handler set to Krumo backtrace above the rendered page. When I access Panelizer under user account settings ( /admin/config/people/accounts ) and attempt to add User Content, the system returns with An AJAX HTTP error occurred. HTTP Result Code: 200 .... In concurrence with this action, error log adds the following line:

PHP Warning: htmlspecialchars() expects parameter 1 to be string, object given in /var/www/html/profiles/panopoly/modules/contrib/devel/krumo/class.krumo.php on line 1071

When I set Devel error handler to Standard Drupal, then I can add User Content without error. I suppose this could be a Panels or a Panopoly problem, but user accounts are the only area where I encounter this problem and only when trying to add User Content. It seems to be a Devel / Krumo issue.