SIP doesn't switch to failover route correctly! SIP-ALG?

Hi!

I’ve made failover setup with recursive routes as is the manual http://wiki.mikrotik.com/wiki/Advanced_Routing_Failover_without_Scripting

http, icmp etc. connections swith normally to failover, at least users do not complain on swithing.
But, SIP-connections to VoIP-providers do not work, until I do command

/ip firewall connection remove [find where connection-type sip]

Actually, SIP-packets go to failover route, BUT these packet bear SNAT source IP of main route still, not source IP of the failover route, as they should!

Any ideas, how to overcome this trouble? Is it SIP-ALG failure?