Certificate not trusted

[loop]

I've been doing some further investigation and here is what I have found so far.

1. The T20 only worked because by default "Only Accept Trusted Certificates" was set to "Disabled". Enabling "Only Accept Trusted Certificates" caused the same problems as the W52P.

2. I tried installing the bought certificate in to the phones and neither phone would register to the server. Looking at the logs from both phones they said "Failed to validate certificate".

3. I installed the bought certificate in to Zoiper on my Macbook and that connected to the server fine.

4. I generated a self signed certificate for the server in question and installed that in to the T20 and the W52P and they both worked fine.

My suspicion is that the Yealink handsets do not understand certificates that have an "intermediate" certificate (otherwise known as chain certificates).

Has anyone had any success getting a Yealink handset to recognise a certificate with intermediate certificates?