1. I never use Angle+Current. By default, I choose Current, unless the reverse lookup is weak, then I use Angle. Angle+Current are just the angle and the current value added together. But negative values can occur on the Angle-RA or the Current-RA values, as well as negative values in Current or Angle when the baseline is used.
2. I suspect that because you used angle, the results come down to the difference between LEAD and LAG. If I put in a frequency and the current lags the voltage, it is positive (for sake of argument); but if the current leads the voltage, then the value is considered negative. Another way of looking at it is that when you look at a circle, 90deg = -270deg.
For more details, please check the link: