Failover Mikrotik

tenho um mikrotik configurado com failover e sempre que há a troca da internet, apenas meus telefones IPs que estão registrados em um pabx remoto não atualizam a rota.
Sempre que um link cai preciso acessar o mikrotik e limpar as conexões com esse PABX em Firewall - Connections para que o registro seja normalizado.
Há alguma configuração no mikrotik que possa gerar esse problema?

English translation using Google Translate:
I have a mikrotik configured with failover and whenever there is the internet exchange, only my IP phones that are registered to a remote pbx do not update the route.
Whenever a link goes down, I need to access mikrotik and clean the connections with this PBX in Firewall - Connections so that the registry is normalized.
Is there any configuration in mikrotik that could generate this problem?

Please post in English.
I have added a machine translated English version.

The whole forum is in English
Using 1 common language will help you get an answer a lot faster.
Also, search engines will be able to pick up your question (and responses) a lot easier in case others have the same issue.

/ip/firewall/service-port/disable sip

Explanation: https://wiki.mikrotik.com/wiki/Manual:IP/Services

Study a bit about SIP Helper and SIP ALG to better understand this configuration.