Configure option '--with-ssh1' breaks openssh-7.3p1

[rl]

My pc runs Scientific Linux release 6.8 (Carbon),
Kernel 2.6.32-642.3.1.el6.i686,
all patches applied.
After unpacking, running   ' -/configure '
(just that, no other params), then
' make; make install DESTDIR=`pwd`/DESTDIR '
and running sshd from there: the call
' DESTDIR/.../bin/ssh host102 '
succeeds ( authentication with id_rsa ; host 102 is localhost
where the new sshd runs).

But running ' ./configure --with-ssh1 ' in a fresh
unpacked openssh-7.3p1 directory,
then the same as above: the sshd starts,
but calling the ssh does not succeed.

I see the following:

sshd:
/Data/openssh-7.3p1/DESTDIR/usr/local/sbin/sshd -p 222   -f \n
DESTDIR/usr/local/etc/sshd_config

ssh:
./ssh -vvv -p 222 -F DESTDIR/usr/local/etc/ssh_config host102

OpenSSH_7.3p1, OpenSSL 1.0.1e-fips 11 Feb 2013
debug1: Reading configuration data DESTDIR/usr/local/etc/ssh_config
debug2: resolving "host102" port 222
debug2: ssh_connect_direct: needpriv 0
debug1: Connecting to host102 [192.168.2.102] port 222.
debug1: Connection established.
debug1: permanently_set_uid: 0/0
debug1: identity file /root/.ssh/id_rsa type 1
...
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_7.3
ssh_exchange_identification: read: Connection reset by peer

/var/log/messages:
Aug  2 17:35:07 host102 sshd[7449]: Server listening on 0.0.0.0 port 222.
Aug  2 17:35:07 host102 sshd[7449]: Server listening on :: port 222.
Aug  2 17:36:03 host102 sshd[7455]: error: buffer_get_bignum_ret: \n
incomplete message
Aug  2 17:36:03 host102 sshd[7455]: fatal: buffer_get_bignum: buffer \n
error


The code after line 1111 in sshd.c (buffer_get_bignum) seems to be not 
adequate any more.
I suppose the error will also show up on Centos.

Best regards
Rainer