When I record existing tracks get recorded into new tracks

From N-Track Wiki

The problem is known as bleeding of the audio output back into the newly recorded tracks. Make sure you've disabled the wave output as a recording source using the soundcard's mixer or windows volume control: run the volume control from Start menu/accessories/multimedia, choose options, select the soundcard and click on the recording radio button and check that all the "show volume control for " checkboxes are activated, then click on OK. Now make sure that only the desired recording source (i.e. line in or mic in) is activated. Please read the "Getting started/Setting the recording level" help topic for further info. Some older soundcards don't allow to disable wave out as a recording and playback source independently. With this cards, if you disable wave out as a recording source it will also be disabled as the playback source, and you won't be able to hear the old tracks while recording a new track. If you have a soundcard that behaves this way you may consider buying another soundcard. A few other suggested soundcards are listed in the FAQ topic What is the best soundcard to use with the program?.