The length of an RSA signature sent during the handshake

[JCA]

I have noticed that OpenSSH clients (at least version 5.1p1)
occasionally send an RSA signature during the handshake phase such
that if the RSA key pair used to generate it happens to be associated
to an N-byte long modulus, the signature is N - 1 bytes long. My
question is, Is this behavior correct? I mean, an RSA signature is an
unstructured byte string, and therefore any leading zeros should be
considered part of the signature, and a signature created with an RSA
key pair such that its associated modulus is N bytes long ought to be
N bytes long as well.