Dave Arquati wrote:

which station is it?
Forest Gate.

Let's rephrase a little: always touch in when you enter the area
covered by pre-pay (the tube, plus some extras).

At a glance that isn't actually the implication of all the literature that
I've seen which talks about the "start" and "end" of "your journey" - who
honestly considers the rail and tube parts as separate journeys? Plus it's
not always easy to find the point to touch in on an interchange platform,
especially when you're diving across the platform at Stratford.

And posters at National Rail stations declaring that "Oyster pre pay is not
valid from this station" reinforces the passenger's conception that they are
*not* a pre pay user.

This could be the basis of a publicity campaign to avoid all this
confusion - define appropriate parts of the network as an "Oyster Area" or
something like that, and tell people to always touch in and out of Oyster
Area. Where there are validators for Tube/rail interchange, e.g. Highbury
& Islington, then there should be a big, clear notice (which people can't
help seeing) that says that you are entering/leaving an "Oyster Area".
("Have you touched in/out?" - like the congestion charge reminder road
signs "Have you paid?".)

Taking Forest Gate, the specific example at hand, the entry point is
Stratford (Liverpool Street is not a problem due to barriers between rail
and tube) and it gets very complicated trying to partition off an Oyster
Area that works because of a mixture of cross-platform interchange between
the Central Line, DLR and suburban services on extremely thin platforms, the
Jubilee Line in a separate part of the station gated off, one tunnel
ostensibly serving as access to the Jubilee line but also to northbound
North London Line services as well as being another way to switch platforms
and so forth. And Stratford does not have much room for clear info posters
(it's bad enough trying to work out if the train on the platform calls at
your station in peak hours) to make it clear where you do and don't need to
swipe in.