Right The "official " answer is as follows; LUL UTS gates 'know' that a NR ticket has been presented from the coding in the NR part of the ticket. NR tickets are always returned to the customer in case the ticket has remaining NR validity/availability.
This return happens even when there is no remaining validity on the ticket.
In efect you bought a Zone 1 return. The destination station is not printed on the ticket, you asked for Tower Hill so that confirmed to the ticket seller that you were travelling in Zone 1
When we used to do fraud surveys on th tube, we used to have to ask where customers were going to, so that the planners could calculate the number of fraudulent and non fraudulent journeys being undertaken on a specific day. Before the extension of UTS gating to the outer zones, a lot of people only carried tickets that would get them in and out of the gates in zone 1. Aldgate East on the 1/2 boundary was always a good place to check and there was a general panic on many trains as we got on as the train as it was about to leave going catching all those going a long way east on zone 1 tickets ;D, The other common scam was using a zone 3 ticket right through from say Walthamstow to the Clapham/Tooting area as start and finish were both in Zone 3, they conveniently forgot that you had to travel through zones 2 and 1 to get to 3 again ;D.
The other common scam was using a zone 3 ticket right through from say Walthamstow to the Clapham/Tooting area as start and finish were both in Zone 3, they conveniently forgot that you had to travel through zones 2 and 1 to get to 3 again ;D.
Oddly, the fare charged on an Oyster pre-pay from Walthamstow (z3) to Heathrow/ Hounslow (z4-6 other side of z1) is the same as avoiding zone 1.
Nothing odd about your experience quiz partner ;D Acton Town is a LU station so the journey you made was using a LU not NR issued ticket. You effectively paid for a journey from Acton Town to anywhere in Zone 1 and the gate at Victoria correctly kept your ticket, if you had alighted at Earls Court or Aldgate East the same thing would have happened. However, if you had journeyed on to Kings Cross without going through the gates at Victoria, your ticket would have been returned by the tube exit gates at Kings Cross and you could have got the H&C or Circle to Moorgate and changed there and and then gone to London Bridge for example where you ticket would have been retained by the gate. It doesn't matter which Zone 1 station you exit from, if you have a LUL isued ticket the gate will retain it, except at Kings Cross which as far as I know, is the only Zone 1 station where you have to use the gates to continue your journey by LUL services.
That is a different scenario, if you go from the main line platforms you are not changing from one LU line to another. If you have a NR issued ticket to Zone 1 the NR barrier should keep your ticket as you have completed that journey, single tickets are not Zone 1 travel cards. If you purchased a single to Liverpool Street AND Zone 1 it will give it back and you can complete a single tube journey in Zone 1. The LU gate will give you back your ticket ( see previous posts) but will not allow a subsequent re-entry to a LU station with that ticket. If you use the Central line from Stratford to Liverpool Street you do not have to go through any gates to change on to the Circle
And what your reader said about passengers using Zone 3 only tickets (say) to other zone 3 destinations via Zone 1/2 had to be avoided when I used to program NR Quickfare machines. A special override had to be utilised to avoid this problem as the system thought that both the destinations AND travel was all within the one zone.
Wimbledon has a national rail ticket office any tickets issued by national rail are not kept by the U.T.S gates if you attempted to use the ticket again it would not work as the gates would reject the ticket as already used.
And what your reader said about passengers using Zone 3 only tickets (say) to other zone 3 destinations via Zone 1/2 had to be avoided when I used to program NR Quickfare machines.
A very unusual fare applies to me when I use a z3 travelcard (with pre-pay when I use it from one zone 3 station to a z3 station after passing through z1 and z2. When I travelled from Walthamstow to Ealing Broadway, it deducted £1.10 from my pre-pay and when travelling from Wood Green (z3) to Pinner (z6 on the other side), it deducted £1.30.