I've since come across even more 'rules' which were preventing proper DW operation.
It depends on the the content of the page being saved. If the page contains words or phrases or sequences which are blacklisted in the OWASP rules within ModSecurity, the page won't save.
The new rules that have been found are 941310, 932100, 932105, 921110.
Given that the OWASP system is ubiquitous in the hosting-provider world, I'm guessing that others must be having problems with it,
It's hard to know what can be done to get around it, as it's obviously not the 'fault' of the DW system. But perhaps someone can think of a workaround? As h4cking prevention becomes more and more necessary, I can only see this syndrome getting worse in the future.