I've got a 4507R with 2 SupII+10GE modules for redundancy. 1 uplink trunk is connected to the 1st module, and another connected to the 2nd module. According to the docs, STP is preserved between Sup-engines, in SSO mode. However, when I pull out the 1st sup-engine to simulate a failed sup-engine, from the console of the 2nd sup-engine, I can see that spanning-tree is in learning mode. Is there any specific configuration I'm missing out to preserve the STP state?