Lew 1 wrote:

For a while, I thought that "London Thameslink" as a destination was always
rejected by the new Blackfriars gates, however since then I have found that
every ticket I try to use - be it a Travelcard or to another destination
requiring an Underground change in London - is rejected.

I am now certain that the gates there are set up to reject any ticket bought
with a Young Persons Railcard, as when I go through the manual gate, the
staff always want to see my photocard and not even on-board staff ever ask
to see that! (I keep it hidden unless requested, because I absolutely hate
the photograph on it)

Assuming I am right (and I think I am, as I have seen tickets bought at the
same machine at the same time but without the railcard discount get through
first time), is this the only gate set-up in London that requires Railcard
holders to use the manual gate?

That's odd. I've used London Blackfriars semi-regularly over the last 18
months (including earlier this week) and as a Y-P ticket holder I've
never had any problems with the gates.

May I ask from where you usually buy your tickets?