I don't dispute the observation, but neither the original code nor the patch makes sense.
At that line, handleUploadProgressResults is NOT called; it's a reference which will be non-null, hence the Boolean will be true. It's a convoluted way of expressing 'true'.
That argument to XMLHttpRequest() *should* be true - false makes the request blocking (synchronous), which is always a bad idea as it can hang the browser. If false makes the code work, something else is broken. Perhaps there is some global variable that should be in a closure.
This needs more investigation...
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