With two or more tuners, you have to go to that channel in the EPG then go back to the MYTV screen. The button will change to stop recording.
That is what I have to do.
I remember this also confused me at some point. I wish that would be renamed "Stop Recording" when it is in the process of recording, but it is not a big deal. Just a communication issue really.
That does sound more straight forward. I always get asked by family members if its a good idea, because to them it sounds like its deleting the recording.