This is expected behaviour. You can override these decisions to a limited degree with load balancing rules. A full description of these rules is available in the documentation PDFs.
We have not been able to load balance the three 5520 SH's in a true round robin fashion using the IC's. What we have observed was that all the connections would be going to one SH until it maxed out the TCP connection and then they would get changed to another SH.
