It works because of luck. What happens is that the last packet received by the PoP is the endpoint that gets the next packets. Thus, host A sends a packet to the PoP and all inbound packets for that tunnel are send to host A. Then when host B sends a packet to the PoP all inbound packets come back to host B. Hence, as long as host A and B have some time between requests (typical on mobile platforms) everything is smooth. But even if they send packets quickly after each other, TCP retries will cause the endpoint selection to flip-flop so much that at one point the packet will arrive at the correct host. Thus while it "works" it is purely because AYIYA is a per-packet protocol. With a too high-frequency of flip-flops between addresses the PoP will kill the tunnel though, thus don't configure it that way, just use a second tunnel.