There were some problems with the old recompute mechanism where features could be set as touched but the tree view didn't show this with the overlay icon. This is because the mustExecute was not correctly implemented or not implemented at all. Then a regression was introduced with v0.17 where objects are superfluously recomputed and thus took a lot of time.
Thus, the recompute mechanism has been reworked to be more robust against possible incorrect implementations of module feature and to reduce superfluous recomputes.
The misbehaviour in FEM now just demonstrates that things work as expected.
To restore the old behaviour you only have to change a single line:
In FemMeshObject.cpp declare FemMesh not as Prop_None but as Prop_NoRecompute or Prop_Output.