[Developers] Cannot read arbitrary property on sandbox

[Will Moffat]

Hello,

This query:
{
   "/people/person/height_meters" : null,
   "id" : "/user/willmoffat/apps/HelloWorld"
}

is OK on otg - http://tinyurl.com/55v6dz
but fails on sandbox- http://tinyurl.com/5v6jls

"You must only delegate enumerations to enumerations"

What's going on?
--Will

(yes, I know it's weird that my application has a height, it's just  
for testing)