[c-nsp] HSRP failover/failback question

[Randy]

I've got an HSRP setup between two 6500's.   Today the primary active 
router's sup took a dump and failed over to the standby.   The blip 
caused the standby router to take over the HSRP gateway on each VLAN as 
expected.   However once the failover was complete on the primary router 
it *immediately* took over the GW's again.   And of course, before it 
had a full routing table so there was several minutes of blackholing.   
I thought we'd be protected from this with the following config, but I 
guess not:

PRIMARY ROUTER VLAN X:
  standby version 2
  standby 0 ip x.x.x.x
  standby 0 priority 150
  standby 0 preempt delay minimum 600

SECONDARY ROUTER VLAN X:
  standby version 2
  standby 0 ip x.x.x.x
  standby 0 preempt delay minimum 600

What am I missing?

Thanks!

~Randy