The problem is that e() always returns a different hash reference

Ah, that's it! I understand.

Please don't use &e to call a sub, use e() instead - you might get surprising results otherwise.

Agreed. I had first %{ e }, but this was (of course) interpreted as hash variable %e, so I replaced it without much thinking by %{&e}. You are absolutely right that %{e()} would have been the better choice.