Using code from changeset edf1fbcb2745 (November, 2011 release) the code in AsyncFileUpload.cs:488 (ReceivedFile method) doesn't take into account extreme nesting. Can be fixed by changing existing line
if (uploadedFile.Replace("$", "_").Replace("_ctl02", "").EndsWith(sendingControlID))
to
if (uploadedFile.Replace("$", "_").Replace("_ctl02", "").EndsWith(sendingControlID.Replace("_ctl02", "")))
if (uploadedFile.Replace("$", "_").Replace("_ctl02", "").EndsWith(sendingControlID))
to
if (uploadedFile.Replace("$", "_").Replace("_ctl02", "").EndsWith(sendingControlID.Replace("_ctl02", "")))