Paul Corfield wrote on 14 December 2012 13:38:30 ...

Oh and while we're on this subject please tell me what fool proof
system Paris or Berlin use that prevents exactly the same problem
happening to tourists? Last time I used a bus in Paris I was turfed
off a bus that was short turned. No one told me what I or anyone else
had to do when the next bus turned up.

In Paris, the standard single-journey "t+" ticket is valid for a journey
made up of several bus segments, so presumably you are meant to validate
it again on the next bus, as you would do if you were changing routes.
I'm not sure whether the system would regard that as a breach of the
no-break-of-journey rule on a single route. I suspect it just checks
against the maximum 1.5 hour journey time.
--
Richard J.
(to email me, swap 'uk' and 'yon' in address)