And what do you expect the result to be?
2 - (-2) = 4
If you want to always subtract the absolute value of a field, you will have to use the Math.abs() function:
event.value = this.getField("Text1").value - Math.abs(this.getField("Text2").value);
This is perfect, thank you!! I was looking for subtracting the absolute value. Your help is much appreciated!