What type of magnetic cards are you trying to write, loco or hico, as The zxp3 is usually delivered set to encode hico cards and the demo code doesn't change this.
Readers generally have a much higher gain compared to the encoder so a loco card encoded on hico settings might work in a reader but not very well.
The demo program uses this line to encode cards:
mag.MagCode(this.cboPrn.Text, "ABCDEFGH", "12345678", "87654321", eject, out msg);
If the reader you have is capable of reading all 3 tracks it should be getting a reading on all three not just track 2 which appears to be happening - again possibly due to loco cards as these are encoded at a 75bit per inch and the other two are encoded at 210 bits per inch. A loco card encoded on a hico setting will probably erase the other two tracks as it goes but track 2 might survive.