I just came across section 3.10.8 ("Queries and Flush Mode") of the JPA spec. It's saying there:

If there is no transaction active, the persistence provider must not flush to the database.

Do you nevertheless prefer that we do a flush on stores where this is implicitly always the case due to their non-transactional nature?

It'd seem a bit contradictory to the spirit of the spec to me. Alternatively we also could provide some special flush mode for that case which does the auto-flush also for non-TX stores / without an active transaction.