It's recording programmes it thinks you may like. Press the My Shows button, then scroll down to the Suggestions folder. Press OK, and you'll find up to 50 recordings that you may like. Suggestions will never stop your planned recordings from happening, and they will get automatically deleted if it needs the space.
If you don't want it to ever record Suggestions, go to Home -> Help & Settings-> Settings -> Recordings -> Suggestions and tell it not to record them.
Explained much better here:
http://store.virginmedia.com/discove...ggestions.html 