Cell with non-manifold triangulation

Hello everyone,

My simulation runs perfectly and it converges both in PISO and SIMPLE mode (i.e unsteady and steady case). However viewing the result, when i apply a slice, the following warning is provided by Paraview:

Generic Warning: In vtkPolyhedron.cxx, line 1836
A cell with a non-manifold triangulation has been encountered. This cell cannot be contoured.

Have i to worry about this? How could this fact impact on my simulation? The comparison between numerical and experimental data is however quite good (at least i would not blame the numerical mesh about discrepancies, considering the turbulence model and the discretizion order i used).

Can you provide some impression about this? Thanks a lot!