The file upload script I wrote early last year for an internal website has been misbehaving oddly on a number of machines. On some machines it consistently works fine, on others it consistently misbehaves. I am having exactly the same problem with YUI Uploader, SWFUpload (2.2 and 2.5a), and Uploadify.

On the misbehaving machines, the progress event (or callback as the case may be) is reporting the upload going far too quickly. It is progressing around 9 or 10MB/s, instead of the 50 or 60kb/s that is actually going on. The progress bar fills up very quickly, and then no more progress events are triggered. A few minutes later the completion event will trigger when the upload is actually done.

I must emphasize that the file upload does proceed normally, even though the progress being reported is very wrong.

The progress events are reporting a correct file size, but the reported amount uploaded is usually way too high, and it appears that it is always a multiple of 2^16 (65536).

I'm only having this problem with Firefox 3.5 on Windows XP, all of which have various subversions of Flash 10.

Has anyone heard of this happening, or have any idea what is going on?

(I'm off to go file a number of bug reports, but hopefully someone here has some previous experience with this.)