Creator does not recognise C++11 headers and types

I'm using Qt 5.0.0, and have CONFIG = c+11 in my project's .pro file.

The Kit I'm using has the macx-clang-libc++ mkspec set and my project is using Clang's libc++ instead of the older libstdc++.

I can use the new STL types such as std::unordered map but they are not recognised by the auto-completion and the new headers like #include <unordered_map> are permanently underlined in the code editor as errors.