bsc.extend is not working properly

When modifying nanos6 in a experiment, we should propagate the changes in the chain nanos6 -> mcxx -> nbody, but is not working properly:

nix-repl> (bsc.extend (self: super: {nanos6 = super.nanos6.override { enableJemalloc=false; }; })).apps.nbody
«derivation /nix/store/hcg4dlqg4dssqdciidmzyqndy62jgj1c-nbody.drv»

nix-repl> (bsc.extend (self: super: {nanos6 = super.nanos6.override { enableJemalloc=true; }; })).apps.nbody  
«derivation /nix/store/hcg4dlqg4dssqdciidmzyqndy62jgj1c-nbody.drv»