I have received a bug report for SWFUpload R3. It may be a little while before I can fix it. I was using the trial version of Flash Studio and it has expired. Does anyone want to donate a copy?
You can reproduce the bug using the SWFUpload Forms Demo. This is the demo where the upload doesn't start immediately but waits for you to call the startUpload function (by clicking the Submit Application button.
The bug occurs when you queue up several files and then cancel the 1st file. The other files will begin uploading. This proceeds to trigger all your Handler functions. In the case of the SWFUpload Forms Demo it triggers a post-back when the queue is complete.
SWFUpload R3 Download
I've signed up at a free file host and have posted the current SWFUpload demos. I'll update the file again when I have a chance to fix the bug. In the meantime the current version is available at 4Shared.com. See this post for the latest release.