this simply means that you are forcing the video output to 1080 regardless of what the broadcast is, for example if the program was 720 it would be upscaled to 1080, press the format button on the tivo to change

If your TV is capable of 1080i (an most likely it is) I'd recommend leaving it at that setting. Generally the Tivo does a good job of scaling 576 and 720 line material without making your TV do it. 

BTW, there appear to be some issues with the underlying codes of some TV series, recently, meaning that series links don't always work unless you modify the series pass to record "All plus duplicates". If anyone else has found this, please let me know examples so that I can pass them on.