Yealink T22 RTPMAP Payload Mismatch

[Terry]

Hi,

We have a couple of T22's (firmware 7.70.23.10) which appear to be be using the wrong codec for calls. In the autop file we have

account.1.codec.1.enable = 1
account.1.codec.1.payload_type = PCMA
account.1.codec.1.priority = 0
account.1.codec.1.rtpmap = 8
account.1.codec.2.enable = 1
account.1.codec.2.payload_type = G729
account.1.codec.2.priority = 1
account.1.codec.2.rtpmap = 18

But in the SDP for an outbound call invite I get:

v=0
o=- 20018 20018 IN IP4 192.168.88.64
s=SDP data
c=IN IP4 192.168.88.64
t=0 0
m=audio 11790 RTP/AVP 18 0 4 101
a=rtpmap:18 PCMA/8000
a=rtpmap:0 G729/8000

It should be:

v=0
o=- 20003 20003 IN IP4 192.168.88.92
s=SDP data
c=IN IP4 192.168.88.92
t=0 0
m=audio 11786 RTP/AVP 8 18 4 101
a=rtpmap:8 PCMA/8000
a=rtpmap:18 G729/8000

If I reset and reprovision the phone it will work again as expected but only for a day or so. There are 15 other T22's at this site using the same autoprovision template and firmware and they have no issues.

What can be causing the rtpmap payload mismatch?

TIA