Telling the truth,
you should get a free instance pooling solution. And put your socket factory on top that pooling, this is more flexible than using SLSB to keep open connections. Don't forget, EJB container can always purge out SLSB at any time. So your sock connection will be gone. But put it in a instnace pooling, you can control it, not EJB container.
This gives you better control. And if 3.5.1 fixes the problem, just use it. Why stick with 3.5.0, if you know it is broken?
IBM won't pay you as a QA person.