Given a pipeline script, I configure to execute a build step to build a (existing) job:
The job is triggered successfully, and the pipeline waits for its completion. But, the called build job has a post-build action defined of kind "trigger parameterized build on other project". The pipeline does not wait for the downstream build, only for the first one in the chain which is referenced by name in the pipeline script. It is expected that the existing functionality is used and embedded "as is", thus pipeline waits for completion of complete downstream chain.
Update: this works as a sequence of build jobs linked with Post Build Actions. Triggering the first one via Pipeline, the downstreamed ones are triggered as well, but the Pipeline does not block until completion. This is critical because this prevents migration.