Why does the NIC fail to come up on boot in RHEL5 for s390x?

Issue

• The server has two OSA-Express cards, both using the qeth device driver modules
• On boot, the network interface "eth0" comes up while "eth1" fails, in spite of having the directive ONBOOT=yes:

# cat /etc/sysconfig/network-scripts/ifcfg-eth0
# IBM QETH
DEVICE=eth0
BOOTPROTO=none
HWADDR=00:06:29:FB:5F:F1
IPADDR=9.12.20.136
NETMASK=255.255.255.0
ONBOOT=yes
NETTYPE=qeth
SUBCHANNELS=0.0.09a0,0.0.09a1,0.0.09a2
TYPE=Ethernet

# cat /etc/sysconfig/network-scripts/ifcfg-eth1
# IBM QETH
DEVICE=eth1
BOOTPROTO=none
HWADDR=00:06:29:FB:5F:F2
IPADDR=192.168.20.136
NETMASK=255.255.255.0
ONBOOT=yes
NETTYPE=qeth
SUBCHANNELS="0.0.09a4,0.0.09a5,0.0.09a6"
TYPE=Ethernet

• The interface has to be manually activated and brought up