Thanks for your thoughts, Rodd. Interesting to know that there are similar problems with the 1DsMkIII.
I accept there might be teething troubles with new versions of the (C1) software but, if even Nikon can't get it right with their CCP software, which has now been around for years, and the D3x (4 years?), what hope is there? And it's the random nature of the problem that makes it so difficult to diagnose; I tried again yesterday on my Win 7 desktop with both C1 v6 and C1 v7, and both disconnected and reconnected successfully ten times in succession, whereas it had failed previously in v7 in as few as two attempts. So it doesn't appear to be specifically a Win 8 problem either.
It's also not the cable, which was an obvious potential candidate; I'm using a single 1.5m cable and have tried four different ones, including an unused Nikon one supplied with the camera. I wondered too if it might perhaps be a loose camera socket, as a cable with an 'L' plug at the camera end and a possibly firmer seating appeared to work successfully and repeatedly at first on the Win 8 laptop, then that too failed as previously.
It's less of an issue now I know the workaround and how to re-establish connection if it fails, but the first occurrence was on site with a client watching - it lost connection when the laptop went to sleep, and it took me 10-15min of fiddling before I persuaded it to reconnect, which was somewhat embarrassing. And it really shouldn't happen.