> some bits about how code is run etc and statements that aren't allowed

There's no restrictions on the JS; perhaps you're referring to what it recognizes as "trivial" (and therefore not needing a license)? For example, "trivial" scripts can't define functions.

If it's not working for whatever reason, it's worth asking about it at help-librejs@gnu.org. If it's a bug, then it can be improved upon.