Store copy of GridView in EntitySet

The EntitySet currently stores a pointer to the underlying GridView. I've always understood the GridView to have value semantics, so should we maybe store a copy? In PDELab, we used to store a const ref in a lot of places, and that has bitten us too often to count.

AFAIK, all grids currently implement A GridView as a pair of pointers to the grid and the index set anyway, don't they?