IscsiSocket.ForwardPDUs() doesn't send all data for larger writes. According to Python Docs, "Applications are responsible for checking that all data has been sent; if only some of the data was transmitted, the application needs to attempt delivery of the remaining data." The method needs a way to track how much data has been sent and continue to call socket.send() as required until all data has been sent.
A while loop has been added to track data sent as of V0.60_beta.