I find the use of Oyster on the DLR remarkably unintuitive (and I'm more
than used to many and varied transport systems all over the world).
The validators are very well hidden and signs reminding people to
validate _ I think - woefully inadequate especially compared to the
Tube, where such reminders are almost overwhelming!).

In message , Paul Corfield
writes
I don't know how the system is set up but it sounds to me as if it is
set up to recognise Canary Wharf DLR and Heron Quays DLR as legitimate
interchanges with Canary Wharf LU. In light of the journey and
validations you described it is entirely possible that the Heron Quays
equipment thought you'd be exiting - was "later on" actually within a
short time span from you leaving Canary Wharf?
Now the first time I used Oyster PAYG on the DLR I was making that very
change and I suspect that, whatever happened in this case, that was what
happened to me. The penny didn't drop at the time but that must have
been it (especially since I exited at Cutty Sark and the system thought
I was entering).

If your Canary Wharf / Heron Quays interchange was within a very space
of time then I'd expect a train captain or RCI to recognise what
happened and not levy a penalty fare. The proximity of stations that are
logical interchanges to the Tube makes it a difficult issue to get right
in all circumstances so discretion should be used in assessing what
someone has done with their Oyster card.
Puzzled by what had happened to me, I approached the member of staff on
board the train. To say that he was uninterested would be an
understatement. When I said I was trying to avoid a penalty fare, he
simply shrugged and said "we don't have checkers" (sic).
--
Ian Jelf, MITG
Birmingham, UK

Registered Blue Badge Tourist Guide for London and the Heart of England
http://www.bluebadge.demon.co.uk