I wondered about this one for a while. Every time this certain 2003 server was rebooted, I had to manually bind the target. How annoying.
Today I found out why. Recently, I had converted the iSCSI disk to a windows “Dynamic Disk” so I could easily expand the disk later as needed. The disk stopped mounting automatically after that.
Unfortunately, some googling revealed that server 2003 does not support persistently bound iSCSI disks if the disk is a Dynamic Disk! It is supported in server 2008 but not server 2003. Just one more reason to upgrade.