Comment 42 for bug 990913

I have also noticed this bug on an Ubuntu 12.04 server. The workaround I've come up with is:
* install the backported Quantal kernel (3.5.x) by installing the linux-generic-lts-quantal package
* add the following patch to /usr/share/initramfs-tools/scripts/mdadm-functions:
--- /tmp/a/mdadm-functions 2013-07-01 12:28:46.896519157 -0500
+++ /tmp/b/mdadm-functions 2013-07-01 12:28:55.136677837 -0500
@@ -3,6 +3,9 @@

 degraded_arrays()
 {
+ udevadm settle
+ echo "Waiting for RAID arrays to be ready..."
+ sleep 20
        mdadm --misc --scan --detail --test >/dev/null 2>&1
        return $((! $?))
 }

Note that just adding "udevadm settle" was not enough in my case - the sleep was also required.