It seems that you are correct. I drew wrong conclusions from the fact, that EclipseLink was able to handle my use case.

The orphanRemoval functionality is intended for entities that are privately “owned” by their parent entity. Portable applications must otherwise not depend upon a specific order of removal, and must not reassign an entity that has been orphaned to another relationship or otherwise attempt to persist it.
(https://jakarta.ee/specifications/persistence/3.1/jakarta-persistence-spec-3.1.html#a516)

Please note, that the current behavior can be a little bit surprising (even if it is unspecified!). I would be certainly less confused if either both of the following operation succeed or both fail (by throwing exception?):
1. moving managed node “x” from managed node “a” to managed node “b”,
2. inserting transient node “x” between managed node “a” and managed node “b”.
Currently, operation 1. is doable and works as expected (at least by some people! ). At the same time, operation 2. fails miserably yet silently.

It’s more than sure that some Hibernate users already depend on 1., so it’s likely not an option to change anything here (or is it?). However, if you can, please consider supporting operation 2. too. Implementation will appear to be more consistent, at least in my opinion.

Thanks again!