On BSDI 4.0.1, sshd answers the port but closes the connection before
negotiation is complete.  Replacing the permanently_set_uid() function in
uidswap.c with the one from 3.6.1p2 fixed the problem for BSDI.

harry:/home/u/jsr/development/exper/openssh-3.7.1p1(8)# ./sshd -d
debug1: sshd version OpenSSH_3.7.1p1
debug1: private host key: #0 type 0 RSA1
debug1: read PEM private key done: type RSA
debug1: private host key: #1 type 1 RSA
debug1: read PEM private key done: type DSA
debug1: private host key: #2 type 2 DSA
debug1: setgroups() failed: Invalid argument
socket: Protocol not supported
debug1: Bind to port 22 on 0.0.0.0.
Server listening on 0.0.0.0 port 22.
Generating 768 bit RSA key.
RSA key generation complete.
debug1: Server will not fork when running in debugging mode.
Connection from 192.168.200.50 port 35982
debug1: Client protocol version 2.0; client software version OpenSSH_3.7.1p1
debug1: match: OpenSSH_3.7.1p1 pat OpenSSH*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-1.99-OpenSSH_3.7.1p1
debug1: permanently_set_uid: 30/13
setreuid 30: Operation not permitted
debug1: Calling cleanup 0x8065214(0x0)