It's a perfectly reasonable sort of trap to fall into. I would just point out that you could have debugged it at the client side, simply by printing that same output to a local file or to stdout instead of (or in addition to) sending it to the socket.

If you had done that sort of test before adding the extra parameter to the string, you might have noticed the extra line-feed in the output, and wondered about that -- maybe it would have no effect on what happens at the server end, but I can easily imagine some situations where an extra line-feed (i.e. a blank line) going through the socket could have an effect, which might be bad.