I just had a bit of fright. I went on Qantas's website to see if I'd been upgraded on either of my flights tomorrow only to discover my reservation for the first flight had been cancelled.
I rang Qantas (whose telephone customer service is always excellent) and they not only assured me I still had a reservation but that I had indeed received an upgrade.
The only theory the representative could offer is that I'd logged into the website at the "split second" (her words) the upgrade was going through and I'd caught it after the economy class reservation had been cancelled but before the business class reservation had gone through. A refresh of the web page confirmed I had indeed between upgraded.
"This sort of thing happens all the time with computers," the helpful representative offered. I guess it does if the system doesn't follow the I in ACID :-)