How to chainbuild in a build override?

Hi, I am trying to build a chain of packages in a build override? I.e. a series of packages: A->B->C I set up a build override for A, and B built successfully. Now, I would have expect building C to pickup B from the A-override. This does not seem to apply. C fails to build, apparently because building doesn't pickup "B" from A's build override. Is this a timing issue (Do I need to wait)? Do I have to setup another build-override for B? Ralf