Engine mode overriding custom environment variable, override 1 and not all?

[v3.7.0.4]
When I set a custom environment variable in engine mode, isn't it supposed to override only the specified one?

As far as I can tell all my 7 items are overridden with 1 item? See https://www.screencast.com/t/cjh7OUJJh
(this makes my tests fail since they need values from the other ones too).

Thanks.

At the moment, it's a full replacement of all existing values ... so there is no inheritance inside the value itself.

I agree inheritance would be more useful. It is the way it is simply because of time/complexity constraints.