I noticed a difference between the public and private WPT instances when requesting the details page for the ‘median’ result:
Public:
http://www.webpagetest.org/result/<test_id>/[color=#FF0000]median[/color]/details/
… this works!
Private (v2.15):
http://myprivateWPT/result/<test_id>/[color=#FF0000]median[/color]/details/
… produces a blank index page!
Any hints?