Generalized, from EJB specification on how TX_REQUIRES_NEW behaves in the context of an existing transaction:
In your case
when the executing SLSB1.method() invokes your SLSB2.method() the container does the following
1. Suspends existing transaction (SLSB1.method())
2. always starts a new transaction (SLSB2.method()), and tries to commit this new transaction before sending SLSB2.method() results to the invoker (SLSB1.method()).