Strange behaviour from mkdir()?

[mal content]

Is this expected behaviour (I'm using the mkdir utility
for the example, but the problem occurs using the system
call directly):

# mkdir .
mkdir: .: File exists
# mkdir ..
mkdir: ..: File exists

Now, the unusual one:

# mkdir /
mkdir: /: Is a directory

Shouldn't it say 'file exists'?

The mkdir() man page doesn't say that the function can set
errno to EISDIR and yet that's what's happening here.

FreeBSD 6.0-RELEASE-p7

MC