Not seeing error events on a browser build

Here's what I'm doing:

``` js
var rpc = superagent
.post('http://localhost/pants')
.set('X-Bananas', 'B.A.N.A.N.A.S.')
.on('error', function(error) {
console.log({when: 'event', error: error});
});
```

Then deep in some other code:

``` js
rpc
.send({method:"bananas"}) // this is 409-ing
.end(function(res) { // callback function expects res only
console.log({when: 'end', res: res});
});
```

The error event is never raised, so I only see a log from the .end() callback.

Am I doing something wrong? Is this a browser feature deficiency?