I had NEVER had any problems at all using OAP and u16 concession tickets until last Wednesday against Wolfsburg. I got in, but my mate was stopped and asked to show his ticket outside W16. We used the excuse another mate had used before in a different part of the ground, that his brother had gone on in earlier as he was in the pub and obviously messed up the tickets but the steward was having none of it. Asked him to ring his brother etc, and obviously as most will know there is more chance of an atmosphere in the South Stand than getting signal in or around OT on match day.
Like I said, I personally have never had a problem but though I'd let you know as this only happened last week.
EDIT: Also, the light definitely DID flash orange when I walked through, luckily the woman in the turnstile box was facing the other way.