Register Failed after network change

[pdoerr]

T38G Firmware 38.70.0.115:
Phone registered okay until we updated network (changed router). After this, phone failed to register, even after reboot, power off/on, factory reset. Could register phone by copying settings from failing Account 1 to Account 2 and then register (Account 1 still failed). Finally resolved problem by (i) saving configuration to file, and (ii) restore configuration from file. After this, phone would register okay.
We have about 9 phones, about half had this problem, was able to fix all of them with the file save/restore. Has anyone else seen this problem?