I was in northern China a few years ago, along the Amur River where it forms the border with Russia. I had a camera, another fellow a camcorder. It was a beautiful place and I took a lot of pictures. The fellow with the camcorder had some of the scenes on his tape erased by the police, later in the day after we had returned to the hotel. Pictures of a small unmanned sentry post (wooden, about 3 m high) left over from the days of tension between Russia and China. The police were very polite and apologetic and only erased the tape where the sentry post showed up. I had pictures of the same thing, but they never bothered me. The confusing part was the sentry post had no military value, at least that we could see. Other stuff, like old gun emplacements, they didn't care about, neither a nearby dam that one would think would be of some strategic importance.
I suspect they knew what they were doing was of no value, but if asked by a superior they could say they did something.