No UFCS with nested functions?

[Tobias Pankrath via Digitalmars-d-learn]

Why does the following not work? It works, if I move the 'prop' 
out of 'foo'.

---
struct S {
        ubyte[12] bar;
}
bool foo (ref S s)
{
   static bool prop(const(ubyte)[] f) {
      return f.length > 1;
   }
        return s.bar[].prop;
}
---

Thanks!