In article , Clive D. W. Feather wrote:
You may then ask, does it know whether you decide to go via Mile End
(Z2), in order to make the journey with just one change of train? The
answer is that it doesn't, and would still only charge you the Z34
fare.

Right.

AFAICS there's no way you could be liable for any sort of
penalty fare, either.

Not on the automated system, no. But if there happened to be an on-train
inspection the situation would change.

Why? Assuming you have pre-pay credit on your card, how on earth could
you be doing anything wrong? You 'tapped in', and 'tapped out', what
else were you supposed to do? Possibly the on-train inspector might do
something to your card which caused you to get charged a bit more
for entering the extra zone, but I can't see any way you could be
fined, surely?