On my Oyster I have a Zone 1-2 annual travelcard for the commute from
my home to my regular office. Currently I'm working offsite in
Feltham, though, so in addition to that I have a Zone 3-6 monthly
travelcard.

This morning, on the train from Waterloo to Feltham, an especially
surly ticket inspector asked to see tickets. I gave my Oystercard, the
light on the little machine went green, all fine. Or so I thought.
The inspector asked where I was travelling to, and I replied, Feltham.
He then said, loudly and aggressively, "you only have Zones 1 & 2 on
that Oyster so your ticket isn't valid to Feltham". I told him that
there was also a Zone 3-6 monthly travelcard on it as well. He replied
that no there wasn't, only Zones 1 & 2, and said that I would have to
leave the train at Clapham Junction as my ticket wasn't valid to
Feltham. So I had to get out the paper receipt to show him! After
extended scrutiny, he grunted and accepted that I had a valid ticket as
far as Feltham; needless to state no apology for the public
humiliation, or explanation why his machine hadn't been able to read
it. Of course the Oyster card worked fine on the gates at Feltham, as
it has done every day since I got it.

So what's the problem with those little machines? Are they simply not
sophisticated enough to read more than the main ticket on an Oyster
card?

Patrick