boost::unique_lock doesn't really know whether the
mutex it wraps is locked or not when the defer_lock
option is used.
The boost::recursive_mutex does not expose this
information, so unique_lock only infers this
knowledge.  When taking the lock is defered, it
(randomly) assumes that the lock is not taken.
boost::unique_lock has the following definition:

      unique_lock(Mutex& m_,defer_lock_t):
          m(&m_),is_locked(false)
      {}

      bool owns_lock() const
      {
          return is_locked;
      }
Thus it is a mistake to check owns_lock() in Enter
and TryEnter - they will always return false.