Windows: How to fix broken permission-inheritance?

On our network-shares, we have all kinds of broken permission-inheritance. Just one example: The folder “D:\Shares\PublicRelations” has full access for the groups “PublicRelations” and “HR” (both with full inheritance set). But the folder “D:\Shares\PublicRelations\SomeTopic” lacks the inherited permissions for the group “HR”, even though inheritance is active. This probably happened, when someone added “HR” to…