Tv will only record the current point we started recording

Hello.

On our new Xfinity box, we used to be able to record anything like if we were already on that channel and we start a recording and it started at 5:00 pm it would record that whole thing since we were still on that channel. But now if we record and it 5:15 it will start there even if we go back it won't record earlier. It should record the whole thing as it used to on the old boxes. Is there a way to fix that because we are missing a lot of stuff because it is only recording the point we record at the current time instead of the whole episode.