Have you ever configured a unique dial plan or daylight saving time rule on a phone only to come back later and find that your unique configuration has been replaced?
Perhaps you have a SPA phone registered to an Asterisk, Trixbox, Broadsoft, or other call control device and found that the phone automatically registered to a SPA9000 that you introduced to the LAN for testing?
This is because the SPA9000 locates and then auto-provisions any device that is configured [by factory default] to accept control from a SPA9000 on the same network.
Disable this automatic process as follows using the device's web-ui:
SIP tab > Linksys Key System Parameters > Linksys Key System: no
Provisioning tab > Configuration Profile > Provision Enable: no