My experience:
1) I installed the 22GB one month ago. No XML generated that time
2) Since then, the UK Ford website kept saying that I still had 7GB to download and install but no way to download them (error, try again later)
3) Yesterday, finally, I had success in downloading the 7GB and I installed them
4) After the first part of the install procedure, the Sync said to me "now you can unplug the USB stick; the system will update the next time it will be switched on" (translation from Italian)
5) The XML had been already generated (therefore, it does not need to know that the install has the happy end; to me, the XML is generated just after the transfer of the files to the internal memory of the Sync, without taking care of the real update of the system).
6) This morning I switched the ignition on and the system updated correctly.
7) I uploaded the XML to the ford website but, as expected and as foreseen by Nigel, the website keeps saying that I have still the 7GB to download because there is some time to wait for the batch processes to update the database.