It's an appalling state of affairs, I agree with everyone above.
People are buying tickets in good faith, which are being issued correctly, and then they're turning up to use their tickets and being told that they're invalid.
Now, I accept that the way the railway fares system has evolved is unusual, but these people are trained and paid to do a job, and they're simply not doing their jobs properly.
It's also a sad state of affairs when enthusiastic amateurs like me know more than the people who are paid to do a job do. Yes, I've been a student of rail fares for many years and it's been a subject that's interested me for self-serving purposes (so that I can get a good deal) for a long time, but that's not good enough.
I'm not sure what can be done about this. There must be many people who don't feel confident in standing their ground, even though they're using a valid ticket properly. On another thread we have someone being denied the existence of an all-line Rover ticket by station staff.
I don't think anyone in the industry cares, and that's appalling. Other commentators have noted this - nobody cares about doing things properly on the railway any more. Of course, that's not true, there are many examples of people posting here who work for the railways who clearly do care, but even they are increasingly frustrated by what's going on.
I'm sad because I've always wanted to do my job to the best of my ability and to do it properly and to serve my customers in the best possible way I could. I have never worked for the railways, but it was clear in the "good old days" of the 1970s that most staff took pride in doing a job well. Sadly, that seems increasingly less the case today, and I'm disappointed if not surprised.