I've been using the volume calculation option in the 3d contour option to estimate the contaminant mass. I checked to see if the volume had converged and notice that the volume was going downward with each iteration and did not appear to be converging.
After receiving your question, I checked the calculations and yes there is an error that will cause the program to not converge on a solution. This has been resolved in release 9.2.0.24. I apologize for the inconvenience. We are constantly testing features, but sometimes things fall between the cracks.