Oh, that's why it happens! Good catch! I would say the bug is here then:

https://github.com/elixir-lang/elixir/blob/master/lib/elixir/lib/exception.ex#L288

Maybe we should not use `Enum.at/2` at all? We just need to skip it for the cases the stacktrace is *not* given (i.e. inside the catch part of try in the code linked above).