welcome to the Polycom Community.
As already mentioned => here <= please raise this via your Polycom Reseller to open a ticket with Polycom support.
Please ensure to provide some feedback if this reply has helped you so other users can profit from your experience.
Polycom Global Services
I am unsure if you have raised this already but the new upcoming UCS 4.0.3 contains a fix for this.
Using your example HTML file against the software version no longer reboots the phone.
This will be released shortly and I will announce the public availability within the community.