Roland Perry wrote:
It is clear to me that the specification is faulty in this case.

The failure mechanism would appear to be someone touching in, and
then touching out on a gate but failing to go through the gate. So
they are still "airside", and capable of catching a train somewhere.

This is such a fundamental fraud vector that whoever designed the
system to allow it (while penalising innocent passengers whose
platform was changed at the last minute) should be hung out to dry.

What do you suggest?

Landside validators to confirm you've left the platform.

.... or even an option on the ticket machines to do the same?
Wouldn't even require special extra validators.

#Paul