This isn’t a “bug”, rather it is part of the platform.
If you want to have developers who only work on certain games you could:
Have the developer only create certain features/projects (almost every big development studio will have roles like “General developer” or “Game developer”, then roles like “programmer” or "product developer)
Add them to a game that you own under your own user
Create a group exclusively for developing the parts of the game you want them to have access to (e.g. a map developers group)
The other issue I see is why are you hiring/permitting developers that you aren’t able to trust?