Mesh selections never really die.
While mesh selections are removed from the interface, they never really die. If you save a mesh resource after having made some selections and then reload it, you will see unnamed meshsets that happen to correspond to all your old selections.
Also, I think this is what is responsible for artifacts that appear to be empty rows in qtReferenceItem dropdowns which accept meshsets.
- Load a surface mesh
- Click the selection filter toolbar's "Mesh" button
- Type 's' and select cells on the surface
- Double click the "Extract by dihedral angle" operation and click apply.
- Optionally repeat steps 3 + 4 a few times
- Save the mesh resource.
- Quit modelbuilder
- Re-run modelbuilder and reload