Other issues to be borne in mind include how capping works with rail
replacement services, when gates are in evacuation mode, when tube
passengers are transferred to local bus services and when a station
close to or at a zone boundary is closed and people have to travel
beyond their zone to exit.

Along similar lines, I haven't found out what is supposed to happen when a
bus or tram is taken out of service and you have to board another one to
complete your journey. On the trams if you touch in at the tramstop again
you will be charged but if you don't then your journey history might seem to
be inappropriate if the ticket is inspected. What about on the buses? Do
you have to get the driver to set the validator to check you had indeed just
been on the previous bus?

I submitted a query about this on the Oystercard site but unfortunately the
Oystercard website is unable to send e-mail to the oystercard.com domain,
which makes it pretty pointless their having an enquiry form.