New X11 trouble

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I have three hosts on my home network, hosta, hostb & hostc, and
I'm having connection troubles amongst some of them.

hosta can run remote X11 applications on either hostb or hostc
without issue. hosta can run multiple applications at the same
time variously on hostb or hostc.

hostb can run X11 applications on hosta.  hostb can only intermittently
run applications on hostc.  For instance, when I try to start up an
xterm, running on hostc and displaying on hostb, then most of the time
the start-up will fail with this message:

X connection to broken (explicit kill or server shutdown).

On the occassions when the xterm does start, then I can launch
more X applications in that xterm.

hostc can't run X11 applications on either of the other two hosts.

Now, here's where I'm really confused.  All three hosts have
identical ssh_config files, have identical sshd_config files,
have identical ~/.ssh/config files, and have identical /etc/hosts

ssh_config contains:

    Host *
      ForwardAgent yes
      ForwardX11 yes
      ForwardX11Trusted yes
      Protocol 2
      StrictHostKeyChecking ask

sshd_config contains:

    Protocol 2
    HostKey /etc/ssh/ssh_host_key
    HostKey /etc/ssh/ssh_host_rsa_key
    HostKey /etc/ssh/ssh_host_dsa_key
    PermitRootLogin no
    X11Forwarding yes
    X11DisplayOffset 10
    X11UseLocalhost no
    UsePrivilegeSeparation no
    MaxStartups 3
    Subsystem       sftp    /usr/lib/ssh/sftp-server

~/.ssh/config contains:

    Compression                             yes
    ForwardX11                              yes
    ForwardAgent                            no
    ForwardX11Trusted                       yes

For a short time I had a problem with /etc/hosts on hostc in that
it had listed as one of the addresses of hostc, causing
me to groom /etc/hosts until they looked good, and look identical
across the hosts.

All 3 hosts are running OpenSSH 4.3p1. hosta is a Mandrake 10.1
system. hostb is a Mandrake 9.0 system. hostc is a Mandriva
2006.0 system.

I'm thinking of going back to OpenSSH 3.7.1p2, which ran without
fail ever since I installed it shortly after its release.  The
Mandriva 2006.0 system ran without fail with OpenSSH 4.2p1.
Maybe that would be a good choice.  I'd rather fix the 4.3p1
implementation tho, since it includes improved security over
prior versions.

Any advice?  Thanks....

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