Warning : Unknown element type for UNV export (MSH type 15) - output file might be invalid

This is a duplicate of this post on CFD-online. Basically when exporting the .geo file to .unv with

gmsh.exe <fileName>.geo -3 -order 1 -format unv

I get lots of

Warning : Unknown element type for UNV export (MSH type 15) - output file might be invalid

and FreeCAD folks have recognized this warning as "useless". So either I'm making a mistake or they are right and this warning should be removed?