There appears to be a bug in the NURBS forward solver when you try to make repeat calculations.
To repeat: solve the attached problem in the frequency domain, and keep plotting the reflectance for the same parameters:
Fwd Solver Engine: Scaled Monte Carlo  NURBS
Solution Domain: frequencydomain, R(rho,ft)
Independent Axis: rho at ft= 0.1GHz
Detector Positions: 0 to 5 mm, Number 51
Optical Properties: ua=0.16, us=1.7, n=1.4
Output: R
Keep plotting reflectance (set y axis to Log10 for easier viewing), and the solution is qualitatively the same 5 times (although if you look at the data, it's slightly different). The sixth time the solution is completely different. Every subsequent
solution is wrong, until you reload VTS.
I will try to upload a screen shot and the exported data, but I'm not sure how to do it from here.
