Reproducible. This applies to any of the publishers that appear in the Post-build Actions list as of pull request #15. The reason seems to be this bit of code in BuildFlow:

@Override
public DescribableList<Publisher, Descriptor<Publisher>> getPublishersList() {
    return new DescribableList<Publisher,Descriptor<Publisher>>(this);
}

In other words, as of pull #15 it pretends to support publishers, but the list is always empty regardless of what you do.

Adding a post-build action to start another job to a Build Flow job does not make a lot of sense; it would be clearer and simpler to just add build('thatJob') to your script. However, if the option appears in the UI it ought to work. More to the point, if you configure a downstream job to use the “Build after other projects are built” trigger and point to a Build Flow project, you expect that to either work or report an error; currently it is offered as an option but has no effect, which is very confusing.

Probably the fix is to copy Project.publishers into BuildFlow, returning it from getPublishersList, and editing/overriding various associated methods to match: onLoad, getResourceActivities, buildDependencyGraph, and most importantly submit.

Code changed in jenkins
User: Nicolas De Loof
Path:
src/main/java/com/cloudbees/plugins/flow/BuildFlow.java
src/main/java/com/cloudbees/plugins/flow/FlowRun.java
http://jenkins-ci.org/commit/build-flow-plugin/1a536a0e0beb6d61695316a34f7d17f309fb685c
Log:
[FIXED JENKINS-14411] publisher support
extend Project/Build, not AbstractProject/AbstractBuild
to get full publisher support

For reference: this commit has been reported to cause an NPE for people upgrading from older versions.