As everyone replies to this thread, I do hope they are understanding the default situation, yes? That every client that tunes for a live session reduces the number of tuners by one?
So you have a 4-tuner HDHR device, but you have 3 TVs with clients. But 2 of your TVs are watching content live. However, you appreciate the amazing fast tuning available via Channels' apps, so you have not enabled tuner sharing.
Now, when recordings are ready to start, the DVR sees there are 3 programs set to record. But, because of the nature of HDHR tuners and their HTTP API, it doesn't know that 2 tuners are unavailable until it tries to record that 3 rd program.
End result: do you want the best TV viewing experience, or a great recording experience? Because at the moment technology dictates only one of those is possible. The defaults that Channels sets is for the best live viewing experience. If your primary goal is recording, perhaps other software would suit you better.