Conceptionally a prerelease uses a single chroot environment.
Therefore all dependencies for all packages get installed at the same time.
This might hide missing dependencies in some of the packages.
I am pretty sure that was the different behavior you have been experiencing.
In order to achieve the same behavior as binarydeb jobs each package would need to be build in its own chroot environment which would require much more computational effort.
This would also require that all previous packages can be installed from Debian packages (to avoid installing all build dependencies).
While the goal to make both jobs behave identical is a good one (and we will aim for it in the future) there is currently no way to change the buildfarm in that way.
We will consider this important goal for the next iteration of the build infrastructure but that will not be something we can address in the near term.
Cheers,
- Dirk