OTS11 — register_resource & SubTransactionAwareResource

I'm confused by the behaviour of register_resource with respect to
the SubtransactionAwareResource interface.

From 99-10-07.pdf:

"If the resource is a subtransaction aware resource (it supports the
SubtransactionAwareResource interface) and the transaction associated
with the target object is a subtransaction, then this operation
registers the specified resource with the subtransaction and indirectly
with the top-level transaction when the subtransaction’s ancestors have
completed. Otherwise, the resource is registered as a participant in the
current transaction. If the current transaction is a subtransaction,
the resource will not receive prepare or commit requests until the
top-level ancestor terminates."

This seems to vaguely say that the resource will be registered as a
SubtransactionAwareResource with if the current transaction is a
subtransaction.

However, later in the second paragraph of 10.3.9:

"Certain recoverable objects may want a finer control over the
registration in the completion of a subtransaction. These recoverable
objects will use the register_resource operation to ensure participation
in the completion of the top-level transaction and they will use the
register_subtran_aware operation to be notified of the completion of
a particular subtransaction."

This says pretty clearly that the application has to call both
register_resource and register_subtran_aware to be registered as a
resource in the transaction and to receive
commit_subtransaction/rollback_subtransaction callbacks.

What is the intended behaviour?