Local red-green refinement copies elements
According to the documentation of
Dune::UGGrid::LOCAL new levels will only contain refined elements and closures. However, with red-green refinement there are additionally two layers of copied elements.
This may be on purpose to ease the implementation of adaptive geometric multigrid. Hence, it's either a bug in dune-uggrid or a bug in the documentation of
Dune::UGGrid. In the latter case it would also be interesting if this can be disabled.