Fails to "unset" or invalidate env vars in sbt shell

[combinatorist]

Problem

Suppose:

1. I start the sbt shell.
2. I have an env var set in my .env
3. When I run my project, the env gets imported.
4. Then, I remove or comment out that specific var from my .env file.
5. I run reload in the sbt shell.

When I run again in the sbt shell, the env var is still there (I can tell by its effect).

Workaround

I can only change it by setting new values for it, but I can't unset it. In order to unset the var, I need to exit the sbt shell and start it again.

Request

I'm happy to create a minified example, but it seemed like such an obvious flaw that I wanted to ask first in case it's a known limitation or actually an issue with sbt, etc.