About behavior of arping command

Issue

• When arping without specified NIC is performed on ServerA to eth1 of ServerB(192.168.1.2), why an entry of eth0 is registered in arp cache table on ServerA?
  • ServerA
    eth0: 192.168.0.1
    eth1: 192.168.1.1
    eth2: 192.168.2.1
  • ServerB
    eth0: 192.168.0.2
    eth1: 192.168.1.2

# arping 192.168.1.2
<snip>
# arp -a
? (1921.68.1.2) at xx:xx:xx:xx:xx:xx [ether] on eth0

• When arping command with specified eth0/eth1 on ServerA is performed, you can get response. However, when arping command with specified eth2 that is not connected to any network equipments is performed, you can't any response. Why?

• arping command with "-s" is performed, you can see arp-reply by tcpdump but why is arp cache table not updated?