Well, I think I understand the problem since I have the same.....

When I reboot the sheeva, everything works fine.
But when I do a cold restart (unplug/replug), then the process stalls, I have to do do a manual reset to boot.

The problem occurs when you boot from an SD card.
Adding a double mmcinit command is a workaround for some, but it doesn't work for me.

I really hope someone find a solution, since it is a real problem to manually reboot the sheeva whenever there is a powerloss...