Trying to locate before the begin of a file is accepted without a returning
   error. Run e.g. the following program:

   [...]

   This contradicts with the former semantics of lseek which reports the
   error EINVAL (invalid argument).

   Are these changes intended or is it a bug ?

Interestingly, I just tried it under SunOS, and it succeeds without
error.  POSIX is ambiguous on the subject.