tcpdump captures unexpected packets on secondary(backup) bonding slave

Issue

• When taking tcpdump on each bonding slave, tcpdump captures ping ICMP request/receive packets on both primary and secondary bonding slaves which are in active-backup mode.
• The seq=1 and same id packets can be detected on both slaves and then the subsequent packets are only detected on the primary bonding slave.
• Why are the first packets detected on secondary while primary is working?

bond0         

14:34:15.208148 IP 10.10.10.10 > 10.10.10.20: ICMP echo request, id 46585, seq 1, length 64 
14:34:15.208584 IP 10.10.10.20 > 10.10.10.10: ICMP echo reply, id 46585, seq 1, length 64    
14:34:16.211336 IP 10.10.10.10 > 10.10.10.20: ICMP echo request, id 46585, seq 2, length 64 
14:34:16.211717 IP 10.10.10.20 > 10.10.10.10: ICMP echo reply, id 46585, seq 2, length 64    
14:34:17.235342 IP 10.10.10.10 > 10.10.10.20: ICMP echo request, id 46585, seq 3, length 64 
14:34:17.235686 IP 10.10.10.20 > 10.10.10.10: ICMP echo reply, id 46585, seq 3, length 64    
... 

slave(secondary)

14:34:15.208186 IP 10.10.10.10 > 10.10.10.20: ICMP echo request, id 46585, seq 1, length 64   <<<---
14:34:15.208586 IP 10.10.10.20 > 10.10.10.10: ICMP echo reply, id 46585, seq 1, length 64   <<<---

slave(active)   

14:34:15.208151 IP 10.10.10.10 > 10.10.10.20: ICMP echo request, id 46585, seq 1, length 64   <<<---
14:34:15.208584 IP 10.10.10.20 > 10.10.10.10: ICMP echo reply, id 46585, seq 1, length 64   <<<---    
14:34:16.211340 IP 10.10.10.10 > 10.10.10.20: ICMP echo request, id 46585, seq 2, length 64 
14:34:16.211717 IP 10.10.10.20 > 10.10.10.10: ICMP echo reply, id 46585, seq 2, length 64    
14:34:17.235347 IP 10.10.10.10 > 10.10.10.20: ICMP echo request, id 46585, seq 3, length 64 
14:34:17.235686 IP 10.10.10.20 > 10.10.10.10: ICMP echo reply, id 46585, seq 3, length 64    
...