802.3ad bonding - link down not detected

Issue

We are having a problem on two servers in an Oracle RAC setup. bond0 is configured in 802.3ad (mode 4), but when both cables are pulled, bond0 does not recognise that the link is down. The interfaces show as down, but not the bond0 interface itself.

ifconfig for bond0 still shows RUNNING, but the partners in the bond (eth0 and eth1) do not show this.

It can also be seen in /proc/net/bonding/bond0, where "MII Status" reports "up" for the bond0, but "down" for both eth0 and eth7.

As for the bonding configuration, we are using the following options:
mode=4 miimon=100 use_carrier=0

(I originally tried without use_carrier - but I have just recently tried testing with this after reboot also, and this still showed the same behaviour).