If you request the json representation of a job with running builds, the running builds are not returned in the list of builds in the output.
This is important for us because we make extensive use of the jenkins API in custom information radiators. Because of this change these are unable to display any running build (because we cannot get running builds from the jenkins API anymore).
example: there is a running build on the jenkins CI at the moment:
build 30 of the infra_backend-merge-all-repo job. If you request the json representation of the job:
build 30 is not in the "builds" list