GUI server drops connection to Juju Core API when response contains non-ascii values

If you deploy this stack...

https://raw.github.com/paulczar/charm-championship/master/monitoringstack.sh

...and then visit the GUI and log in, you'll notice that the GUI has problems. It can't show a lot of information. If you go in the console and poke around, and reload the page, sometimes you'll get an error about a reconnecting web socket complaining. If you then go to the network tab (chrome/chromium) and look at the websocket frames, you'll see that the websocket falls over on the Juju side, pretty reliably about 1 second into the connection. http://ubuntuone.com/707jMTdcPvB8fr1r6Gei0G . If you look at it further, you see that the browser is getting a lot of responses from requests to Juju, but never getting a response to the AllWatcher Next call.

Then, if you go to machine 0 and look at /var/log/juju/machine-0.log, you'll see something like this: http://pastebin.ubuntu.com/6247538/

Our pastebins can disappear, so here's the crux. You can see the GUI's request for AllWatcher Next:

2013-10-16 19:56:29 DEBUG juju.rpc.jsoncodec codec.go:107 <- {"Type":"AllWatcher","Request":"Next","Id":"1","Params":{},"RequestId":5}

You can see a lot of other requests and successful responses. Finally, you can see this, which is correlated with the AllWatcher Next request because of the RequestId

2013-10-16 20:05:27 DEBUG juju.rpc.jsoncodec codec.go:110 <- error: EOF (closing false)
2013-10-16 20:05:27 DEBUG juju.rpc.jsoncodec codec.go:172 -> {"RequestId":5,"Error":"state watcher was stopped","Response":{}}
2013-10-16 20:05:27 ERROR juju.rpc server.go:418 error writing response: EOF
2013-10-16 20:05:27 INFO juju.rpc server.go:237 error closing codec: EOF

As far as I can tell, this is Very Bad. It doesn't always happen, but it might always happen at non-toy scale. In that vein, I am trying to verify if https://bugs.launchpad.net/juju-gui/+bug/1238301 has the same symptoms from Juju Core, and will report back here.