Customer needs to change the ring back tone from Default (China) to UK ring tone. After the change, the web page is successfuly saved, but the change does not take effect.
Check the version of the IP phone - The clients version was V100R001C01SPC300.
I tested his the scenario in the lab using eSpace 7950 V200R002C00SPC300. The test was successfull.
After the customer updated the software version, the issue was solved.