Thank you for your test.
        
One of my clients is on Solaris
> curl 7.18.2 (sparc-sun-solaris2.10) libcurl/7.18.2 OpenSSL/0.9.8g zlib/1.1.4 libssh2/0.19.0-20080613
> Protocols: tftp ftp telnet dict ldap http file https ftps scp sftp
> Features: IPv6 Largefile NTLM SSL libz
which puts a file via scp to the local Solaris 10 sshd
> debug1: sshd version Sun_SSH_1.1
and alternatively via sock4 to an unknown remote server which
identifies itself as
> debug1: Remote protocol version 2.0, remote software version OpenSSH_3.9p1

The other client is Ubuntu 7.10
> curl 7.18.2 (i686-pc-linux-gnu) libcurl/7.18.2 libssh2/0.18
> Protocols: tftp ftp telnet dict http file scp sftp
> Features: IPv6 Largefile
which puts a file to the local Ubuntu 7.10 sshd
> debug1: sshd version OpenSSH_4.6p1 Debian-5build1

All of these server versions seem to be older than your OpenSSH_4.7p1 server.
Since curl scp put is working with your setup, it might be a problem
with OpenSSH < 4.7
I'll check the release notes of OpenSSH 4.7.
And I'll try to set up an Server with OpenSSH 4.7 and see if
curl is working with that.
(The UNIX scp command is compatible with all of these servers.)
Received on 2008-06-17