So you are trying to chunck uploads or other cool stuff with Plupload?
Maybe you are making a “video uploader” with chuncked file but on iPad, iOS in general, when adding a video file nothing happens, while adding pictures or other files it works?
The problem is that the iOS device try to compress the video before sending it to the server, you aren’t seeing it now because multi_selection is not set to false (default is true)

var uploader = new plupload.Uploader({
     multi_selection : false
});

if you can afford to have only one upload a time, then switch it to false and try.
You’ll understand immediatly what happens on iOS devices after trying to upload a movie and why it wasn’t working before. 🙂