I agree, my rule is designed to keep them on seperate boxes, however that doesn't make sense if two boxes are already powered up. THis is an exact scenario I had:
2 Hosts running with more than enough power to handle DC2 on either box.
DC2 is not running
I power up DC2
a 3rd ESX host powers up.
DC2 waits for the third host to power up then powers on on this third host.
Now here is the fun part, after DC2 is powered up, DRS migrates all the VMs off of the 2nd host and powers it down.
This is what I find weird. Its not a problem, it's just weird and I was wondering if anyone else has experienced this.