After seven months, I was finally able to isolate the upload problems that have been occurring for songs and profile images. It turns out that the cause of the problem is using a Mac. I got another report from a very helpful person, which means that in addition to Vile he's now the third person who has had this problem using a Mac.
I reported the bug to swfupload at
http://code.google.com/p/swfupload/i...For%20Modified, and will wait for a week to see whether they fix it or not. If not, then I'm going to completely rewrite the upload routine using a different uploading tool.
For now, the feature works fine on Windows. If you don't have access to any Windows computers, feel free to send me the file and I'll upload it myself, after which you can modify the description and other information yourself.