Battlegroups resource error

The battlegroups resource works only when I am not authenticated (i.e. not using my public/private API key pair to authenticate the request). When I use my API key I get an error saying "Invalid application signature.".

Note that my API pair works fine with all other resources.

Here is a sample request I am submitting:

GET /api/wow/data/battlegroups/?locale=en_GB HTTP/1.1
Date: Sat, 08 Sep 2012 14:42:22 GMT
Authorization: BNET ===REMOVED===
Accept-Encoding: gzip,deflate
Host: eu.battle.net
Connection: Keep-Alive

The response I am getting

HTTP/1.1 500 Internal Server Error
Date: Sat, 08 Sep 2012 14:41:40 GMT
Server: Apache
X-Frame-Options: SAMEORIGIN
Vary: Accept-Encoding
Content-Length: 60
Connection: close
Content-Type: application/json;charset=utf-8

{"status":"nok", "reason": "Invalid application signature."}