Fortran90: present() function doesn't work in subroutines

isotoper

I am using Gfortran 4.4.3 on Ubuntu 10.04 operating system.
Can someone explain why the following code works correctly (a):-

program testpresent
real :: a,b,c
call test_present(a,b,c)
contains
subroutine test_present(x1,x2,x3,x4,x5,x6)
real, intent(inout), optional :: x1,x2,x3,x4,x5,x6
write(6,*) present(x1),present(x2),present(x3),present(x4),present(x5),present(x6)
return
end subroutine test_present
end program

works correctly (T T T F F F) while (b):-

program testpresent
real :: a,b,c
call test_present(a,b,c)
end program

subroutine test_present(x1,x2,x3,x4,x5,x6)
real, intent(inout), optional :: x1,x2,x3,x4,x5,x6
write(6,*) present(x1),present(x2),present(x3),present(x4),present(x5),present(x6)
end subroutine test_present

does not. There is nothing in the documentation that says (b) is wrong, and it compiles without error messages.