Using 7 you need to put in all the other details such as phone IP, VLAN, ICP, TFTP server, etc.
Using 9 you put it in TW mode as if you were using a TW server. It short cuts all the other stuff.
Now, having said that, I've also seen this happen when the network interface to the customers DHCP server was set to "Trunking" mode.
The DHCP server would send the IP info that told the phone to switch to the voice vlan and request a new one.
When the phone switched vlans and sent out the second DHCP request, both the customers DHCP server AND the 3300 sent out IP addresses.
The 1st one to get to the phone wins. That was always the DHCP server since it was faster than the 3300.
This caused a boot failure.
Ralph