How can I tell that an ASIFormDataRequest upload failed?

[G S]

I'm uploading to a PHP page with an ASIFormDataRequest.  This typically works, but when it doesn't, there's no indication of that.  The operation's error state is not set.

To test this, I renamed the PHP page that handles the uploads.  Despite this glaring error, the operation winds up flagged as complete with no error.  Anybody know why, or what the best place is to intercept this failure and set the error properly?

Thanks!

Gavin