EU U Support is correct. Registering with CUCM defaults on the device page to login reqd On and must be updated and saved to Off 

Probably not an issue with v7.1.5, but I just had a TAC case with identical issue on our v8.6.2.20000-2 >> 8.6(2a) where RTMT showed an alert for number of reg'd phones exceeded, even though we have a 7,500 endpoint OVA deployment on each node and th...

Also please paste the router config from packet tracer. We need to ensure the step for option 150 wasn't missed in the DHCP pool which allows the phones to pull their configs.