Clip filter tetrahedralizes the whole mesh whenever a complex cell is present
When at least one complex cell such as a polygon, polyhedron, high-order cell, etc. is present in a mesh, the Clip filter will call vtkClipDataSet
internally.
The latter tetrahedralizes the entire clipped dataset, including regular cells such as hexahedra or wedges, which should be left intact or simply clipped.
Before ParaView 5.11.0, only complex cells were tetrahedralized instead of the entire dataset.
This change seems to have been introduced in vtk/vtk!9310 (merged).