RPM build warnings: File listed twice

I was playing with rust2rpm
Long story short, rpmbuild completes successfully, but I get these warnings:

RPM build warnings:
    File listed twice: /usr/share/cargo/registry/is_executable-1.0.1/LICENSE-APACHE
    File listed twice: /usr/share/cargo/registry/is_executable-1.0.1/LICENSE-MIT
    File listed twice: /usr/share/cargo/registry/is_executable-1.0.1/README.md

So I looked to other Rust packages SPEC files, I tried to build a couple of them, and rpmbuild always throws warnings like these.

Is this expected? Can it be safely ignored?