What does "MII Status: going back" on bond# mean?

Issue

• What does "MII Status: going back" on bond# mean?

Sample output:

# cat /proc/net/bonding/bond0 
Ethernet Channel Bonding Driver: v3.6.0 (September 26, 2009)

Bonding Mode: fault-tolerance (active-backup)
Primary Slave: eth0 (primary_reselect always)
Currently Active Slave: eth0
MII Status: up
MII Polling Interval (ms): 1000
Up Delay (ms): 5000     <== updelay's value
Down Delay (ms): 0

Slave Interface: eth0
MII Status: up
Speed: 1000 Mbps
Duplex: full
Link Failure Count: 0
Permanent HW addr: a0:b3:cc:e9:5c:a9
Slave queue ID: 0

Slave Interface: eth1
MII Status: going back      <== this state
Speed: 1000 Mbps
Duplex: full
Link Failure Count: 1
Permanent HW addr: 00:1b:21:8b:62:f9
Slave queue ID: 0
# cat /etc/sysconfig/network-scripts/ifcfg-bond0
DEVICE=bond0
ONBOOT=yes
BOOTPROTO=none
USERCTL=no
BOOTPROTO=dhcp
BONDING_OPTS="mode=1 miimon=1000 updelay=5000 primary=eth0"