Anything originating from or to the PAN interface directly will not match PBF and will always use vr routing table.Since the IPSEC negotiation is done via the external interfaces it might have been the problem with your case where the request was going through the ISP mentioned in the routing table and the reply from the other ISP the below document explains it in detail:
Hope this document helps you.it explains the problems you run into and how to resolve them.Tunnel traffic and traffic originating from the PAN interface directly do not lookup PBF rules and will always follow VR.This is by design.The document specifies how the configurations can be made to get around this problems by configuring two virtual routers.
Kindly give it a try and get back to us if you have any more questions or if you run into any problems.
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