Create a pipeline with the following configuration and run the job.
Create another job (upstream) in the same folder and run it (should see original pipeline is triggered).
Remove triggers from original pipeline, rerun it (to ensure a new config.xml could be generated)
Rerun upstream job
The second run should trigger the pipeline job. What I've done in the past to workaround this is to put in a bogus upstream job in triggers to force a rewrite of config.xml.