Thanks for the advice. It took some effort, but we were able to get ethereal going to monitor the server traffic. There is a definite pattern to the failures. Every one of them coincides with a TCP RST command, like this: 
client > server  HTTP POST
server > client  ACK
client > server  RST

[download]
I don't know enough about networking to interpret what that means, but I can see a one-to-one correlation between those RST's and the 104 status codes in our log.

My best guess is that some firewall/antivirus/router/whatever in between their citrix and our server is examining the content of the traffic and deciding to kill the session because the Japanese UTF-8 data looks malicious.

Does that seem like a reasonable theory? Anyone else know TCP well enough to offer other theories?

Thanks,
Joe

In reply to Re^2: debugging apache response status 104 for cgi script by blahblahblah
in thread debugging apache response status 104 for cgi script by blahblahblah

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