>  EclGrid instance should be created with the "actnum" map from struct grdecl, and not directly from the input deck

I agree.  I don't know precisely when this code will be called but if it is at any point *after* the cornerpoint processing, then we need to account for pinch-outs and similar effects.  The processor also supports a deck with no `ACTNUM` vector at all.  This case is interpreted as all cells (nominally) active, but I don't know if this behaviour is a non-standard extension compared to the commercial simulator.