I have been struggling with this for 2 days since I received my Tascam Ministudio Personal US-32 yesterday. I had it working as soon as I plugged it in, but then the same thing happened to me, and it would start recording track 1 as soon as I tried to record my 2nd track with just vocals. What I just discovered is in the Tascam Ministudio Settings Panel under the Mode Presets it will record everything if you are set to Broadcast (default) mode.
I just set that mode to Talk and it is now working as designed, and it also allows me to play music from my media player without recording that either.
I have no idea how it worked the first time I plugged it in yesterday or what made Broadcast all of a sudden start recording the first track (since Broadcast is the default), but if the Talk setting is the answer, I’m good with it.
Playing with the fader doesn’t seem to be the answer here because that just stops the music from coming to the headphones too and we need the music through the headphones to do our singing on the next track.
I want to also add that there is another Ministudio Creator and there very well may be some other method for making this work on that product, but this seems like it should work on both models.