KeyError: 'file'

[zooko]

I left a large upload running through the WUI overnight. In the morning it was still running, but I accidentally hit the "private browsing" key in Firefox 4 and then hit it again. This seems to have aborted the upload (which was probably still transferring the file from the web browser to the tahoe-lafs gateway and had probably not even begun to upload from the tahoe-lafs gateway to the tahoe-lafs servers). So, I clicked the Upload button again, and to my surprise I got this traceback:

2011-03-31 05:39:07-0600 [HTTPChannel,21,127.0.0.1] Unhandled Error
        Traceback (most recent call last):
          File "/Library/Python/2.6/site-packages/Twisted-10.2.0-py2.6-macosx-10.6-universal.egg/twisted/internet/defer.py", line 297, in addCallback
            callbackKeywords=kw)
          File "/Library/Python/2.6/site-packages/Twisted-10.2.0-py2.6-macosx-10.6-universal.egg/twisted/internet/defer.py", line 286, in addCallbacks
            self._runCallbacks()
          File "/Library/Python/2.6/site-packages/Twisted-10.2.0-py2.6-macosx-10.6-universal.egg/twisted/internet/defer.py", line 542, in _runCallbacks
            current.result = callback(current.result, *args, **kw)
          File "/Users/owhielaclient/tahoe-lafs/support/lib/python2.6/site-packages/Nevow-0.10.0-py2.6.egg/nevow/appserver.py", line 163, in gotPageContext
            pageContext.tag.renderHTTP, pageContext
        --- <exception caught here> ---
          File "/Library/Python/2.6/site-packages/Twisted-10.2.0-py2.6-macosx-10.6-universal.egg/twisted/internet/defer.py", line 133, in maybeDeferred
            result = f(*args, **kw)
          File "/Users/owhielaclient/tahoe-lafs/src/allmydata/web/common.py", line 302, in renderHTTP
            return m(ctx)
          File "/Users/owhielaclient/tahoe-lafs/src/allmydata/web/directory.py", line 202, in render_POST
            d = self._POST_upload(ctx) # this one needs the context
          File "/Users/owhielaclient/tahoe-lafs/src/allmydata/web/directory.py", line 307, in _POST_upload
            contents = req.fields["file"]
          File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/cgi.py", line 520, in __getitem__
            raise KeyError, key
        exceptions.KeyError: 'file'

I'll attach the debugging output that the gateway returned to my browser.