Unity Transport disappears from PackMan UI after downgrading it after changes in dependent Unity Netcode package.

To repro:
1. Download https://github.com/Unity-Technologies/netcode and open sampleproject.
2. Open Package manager.
3. Select Unity Netcode package.
4. Downgrade it to Version 0.1.0-preview.6.
5. [Optionally] Reimport all.
6. Downgrade Unity Transport version to any version below (e.g. "0.2.3-preview.0").

Actual result: Unity Transport is no more listed in Package Manager UI, but is present in manifest.json.
Expected result: All packages from manifest.json are listed in Package Manager UI.