It could be something in the template is overwriting the custom config done in the phones interface. Note that the phones usually to check their config against the server and certain intervals (they vary between makes and models).
The simplest way to check if this is what is happening is that remove the Provisioning Link from the phones interface so that it does not re-download the config, if it stills resets these settings, then it is clearly a Htek question.
It is worth noting that when classifying phones as "supported", we do not test any of the add-on modules apart from the sidecars.