Kerberos borks on packet type 34

Here's the setup server_a is a perfectly working KDC running 10.3.4 Server that has no problems. I can use single signon to my hearts content with it. server_b is running 10.3.4 (not Server) and I want to be able to single sign on to it. I use kinit to get myself a ticket from the KDC. That works and I now have a ticket (checked with klist). I then do an ssh to server_a. That works and I now have a host ticket for server_a. I try and use ssh to log on to server_b. It fails with "Disconnecting: Protocol error: didn't expect packet type 34" but a klist tells me that I now have a host ticket for server_b. I get an identical error if I try using 'sftp' instead of 'ssh'. Anybody seen this before? Tony