Engine Plate jettison doesn't work

[Docker]

In the previous release, it was possible to do a Saturn V style "dual plane separation" by placing an upside-down structural tube to an engine plate node and using the plate's 'jettison' action (using a right-side up tube or decoupler would stop the engines from producing thrust). 

This still works exactly the same way except in 0.1.1.0 the jettison doesn't actually separate the tube from the engine plate and it just floats there. 

[Streetwind]

That is because engine plates are no longer decouplers like they were in KSP1. The "jettison" action detaches the engine plate's shroud. It does not decouple the node below it. That's why it is specifically not named "decouple", but rather something else.

In order to decouple a stage below an engine plate, you must use a stack decoupler or stack separator. (Conveniently, both of them are hollow rings, so your desired setup will still work.)

My best guess as to why that was done is that the engine plates with built-in decouplers in KSP1 were essentially "upside down" - the decoupler stayed with the stage it was attached to, rather than the stage that was decoupled. This went against all other ingame logic, confused the heck out of the Engineer's Report in the editor, and had the potential to mess with fuel flow logic in certain edge cases. It made sense to streamline them for KSP2.