If I have a job that is parameterized, and I try to remove parameters from its config.xml via HTTP post to JOB_URL/config.xml, nothing happens.
The correct config.xml is uploaded (this can be seen in the JOB_URL/config.xml page), but there seems to be no effect on the interface.
Manually reloading configuration from disk in Jenkins Management after uploading the new XML will put the correct options there.
I've only tested this using python_jenkins, but it really only does an HTTP post:
XML files attached.
Reproduced in 1.528 and 1.565.