Perhaps I'm misunderstanding this, but I've noticed something strange when using WTMASS in the bdf file. In my case, my FEM weights are in pounds (force) and I specify a WTMASS parameter in the bdf file (0.00258). In HyperSizer, I choose "FEM densities and mass elements are in MASS units."
When I size the structure, the nonstructural mass on the pm1 card is in the right units (lbs force/sq in), but then when I hit the "Update FEM" button, all the nonstructural masses in the pm1 file are multiplied by the WTMASS parameter. I have only noticed this now because I only use the "Update FEM" button on the first of 3 or 4 runs, so the remaining runs correct the first. I noticed then when using HyperFEA because I'm assuming its updating the FEM each iteration.
Am I misunderstanding the way HyperSizer uses the WTMASS parameters?