Eos unresponsive to self-made OSC messages

I'm playing around with writing my own software that will send OSC to an Eos console and running into a bit of a stumbling block.

When I connect via TCP, I can see the connection noted in the diagnostics tab, but get absolutely no response from the console when I try to send OSC messages.  Looking at the traffic in Wireshark, I can see them making it to the target computer, and it looks (to me) that the messages being sent by my program are identical in form to the ones that Eos is sending out, as well as messages that come from MLA that I know work.

I noticed that messages coming from the console are prepended with four bytes that show the length of the message, but if I prepend those four bytes to my message the console still doesn't react.

If I fire up StringTheory and try to send messages that way, I also get nothing.  Oddly, though, if I send them via UDP I see the received message in tab 99, but only if it's UDP directly to that computer's IP (UDP to a broadcast address gets no response), and "/eos/ping" isn't answered with "/eos/out/ping".

Is there some extra step to setting up a TCP connection with Eos that I don't know about?