Disable "recall" transfers

[Luke Escude]

It's definitely happening due to direct transfers - our PBX (Asterisk, with our own cloud PBX software managing it) properly handles callbacks from call parking timeouts.

Apparently the phone is receiving a 503 Service Unavailable from the PBX in a NOTIFY event, which triggers this behavior.

Can we get an option to completely disable recall? Or simply ignore the 503 in response to a transfer?

This doesn't happen with any other phone manufacturer, which is weird.

SIP RFC 3515 s. 2.4.5:
A minimal, but complete, implementation can respond with a single
NOTIFY containing either the body: SIP/2.0 100 Trying
if the subscription is pending, the body: SIP/2.0 200 OK
if the reference was successful, the body: SIP/2.0 503 Service Unavailable
if the reference failed, or the body: SIP/2.0 603 Declined
if the REFER request was accepted before approval to follow the reference could be obtained and that approval was subsequently denied
(see Section 2.4.7).