1. Visit /pipeline-syntax/
2. Select an item (e.g. bat)
3. Wait for the server to restart
4. Switch the drop down to something else
5. The area for the selected item is cleared
6. The area for the new item won't be updated
7. If you switch to something that's already been cached, the area will be updated to the cached item

Expected results:

There is an error about the session, it should be reported to the user.

Actual results:

prototype.js:1585 POST http://localhost:9001/$stapler/bound/227c70ea-aa50-4471-b154-874a9ad2cae4/render 404 (Not Found)prototype.js:1585 POST http://localhost:9001/$stapler/bound/227c70ea-aa50-4471-b154-874a9ad2cae4/render 404 (Not Found)
request @ prototype.js:1585
initialize @ prototype.js:1550
(anonymous) @ prototype.js:452
klass @ prototype.js:101
proxy.(anonymous function) @ bind.js:48
renderOnDemand @ hudson-behavior.js:554
updateDropDownList @ hudson-behavior.js:1127
ListPicker._handleKeyDown 

While the component in question is workflow-cps-plugin, the entire stack trace is core (stuff I've been playing with for my other work). This report is based on 2.166 (clean) and the latest pipeline plugins*.

*It's frustrating that I can't search by github's repo name in the installed plugins list, but that's something I might fix elsewhere.