Arguments using a validator to transform the internal value (ie, uid => username) were not getting transformed before they were used in Peek Summary argument links, or before they were passed to the child views.
"Strict warning: Creating default object from empty value in view->init_pager() (line 660 of /shared/vash/sandboxes/white/base/www/sites/all/modules/views/includes/view.inc)." on pages where peek summary output was rendered.