ac.error() sends an empty response to binder

I have a mojit with a binder that tunnels a database query to its server-side controller. In the binder, the response is processed by a ModelList hooked to a DataTable. Everything works fine as long as there are no errors in the database. In the case of an error, everything works up to the point when the controller calls ac.error(err), where err has the following form (as I get it from pg and as rendered by console.log in the server):

{ [error: column "test" does not exist]
  name: 'error',
  length: 97,
  severity: 'ERROR',
  code: '42703',
  detail: undefined,
  hint: undefined,
  position: '56',
  internalPosition: undefined,
  internalQuery: undefined,
  where: undefined,
  file: 'parse_relation.c',
  line: '2655',
  routine: 'errorMissingColumn' }

I haven't tracked all the goings-on between the call to ac.error() and the moment when stuff gets written to the socket, but at the other end of it, I see

POST http://bfs.observercentral.net/tunnel 42703 (unknown) io-base.js:737
IO.send io-base.js:737
Y.io io-base.js:903
TunnelClient._makeRequest mojito-tunnel-client.js:74
TunnelClient.rpc mojito-tunnel-client.js:68
Y.namespace.Dispatcher.rpc mojito-dispatcher.js:150
(anonymous function) mojito-dispatcher.js:216
(anonymous function) mojito-client-store.js:223
retrieveFile mojito-client-store.js:84
ClientStore._getType mojito-client-store.js:346
ClientStore.expandInstanceForEnv mojito-client-store.js:190
ClientStore.expandInstance mojito-client-store.js:152
Y.namespace.Dispatcher.dispatch mojito-dispatcher.js:196
MojitoClient.executeAction mojito-client.js:684
MojitoClient.init.Y.Array.each.(anonymous function) mojito-client.js:427
MojitProxy.invoke mojito-mojit-proxy.js:275

while mojito-output-buffer reports:

error: (mojito-output-buffer): Error executing: 'undefined':
error: (mojito-output-buffer): column "test" does not exist
error: (mojito-output-buffer): 
error: column "test" does not exist
    at Connection.parseE (/home/bfs/mojito/bfs/node_modules/pg/lib/connection.js:526:11)
    at Connection.parseMessage (/home/bfs/mojito/bfs/node_modules/pg/lib/connection.js:356:17)
    at Socket.<anonymous> (/home/bfs/mojito/bfs/node_modules/pg/lib/connection.js:105:22)
    at Socket.EventEmitter.emit (events.js:95:17)
    at Socket.<anonymous> (_stream_readable.js:745:14)
    at Socket.EventEmitter.emit (events.js:92:17)
    at emitReadable_ (_stream_readable.js:407:10)
    at emitReadable (_stream_readable.js:403:5)
    at readableAddChunk (_stream_readable.js:165:9)
    at Socket.Readable.push (_stream_readable.js:127:10)

This raises a few questions:

What's up with the undefined id in OutputBuffer? What does it mean and how do I define it?
What's that unknown request status of 42703? Is that an intended value?
Where did the error go? The response has no body.
Why does the ModelList's error event not fire immediately? Instead, it fires like this half-a-minute later:

server transaction error: Unexpected token u yui-base.js:5779
INSTANCE.log yui-base.js:5779
(anonymous function) SamplesBinderIndex.js:843
Y.Subscriber._notify event-custom-base.js:1313
Y.Subscriber.notify event-custom-base.js:1342
Y.CustomEvent._notify event-custom-base.js:1005
Y.CustomEvent._procSubs event-custom-base.js:1131
CEProto.fireComplex event-custom-complex.js:230
Y.CustomEvent._fire event-custom-base.js:1078
ET.fire event-custom-base.js:2233
(anonymous function) model-list.js:612
(anonymous function) SamplesBinderIndex.js:245
OutputHandler.error mojito-output-handler.js:169
TunnelClient.rpc.cfg.on.failure mojito-tunnel-client.js:58

What is that "Unexpected token u" business? Is that Y.JSON trying to parse an empty body?

I will appreciate any clues for how to debug it further, or for how to do it right.

YahooArchive / mojito

ac.error() sends an empty response to binder #1379