creating namedqueries is reworked in 5.2 and it seems only the values of JPA are allowed...
Initially its set correct in org.hibernate.internal.AbstractSharedSessionContract.initQueryFromNamedDefinition(Query, NamedQueryDefinition) as there the hibernateflush mode is set.
But in org.hibernate.internal.SessionImpl.initQueryFromNamedDefinition(Query, NamedQueryDefinition) its set eventually with the JPA mode on the query in this codepart:
As end result by default hibernate actually doesn't support the annotation MANUAL anymore.
Not sure if this is what should be, if there is a work around (that I didn't find yet, except for setting it on the created query again)
If this is intentionally then at least the FlushModeType.MANUAL should be marked as deprecated...