openssh unix dev - Oct 2011 - scp with different users

This may be a dumb question, but is there any reason why
  scp a at b:c d:
fails, where
  scp a at b:c .
  scp c d:
succeeds?

I get "Host key verification failed.". I'm using nothing more
complex
than RSA authorized_hosts based authentication.

I'm seeing this on openssh-client 1:5.8p1-1ubuntu3 and
OS-X 10.6 OpenSSH_5.2p1, OpenSSL 0.9.8r 8 Feb 2011.

-- 
Alex Bligh

Alex Bligh wrote:
> why
>  scp a at b:c d:
> fails, where
>  scp a at b:c .
>  scp c d:
> succeeds?
The former copies from c to d while the latter first copies from c to .
and then from . to d.


//Peter