I was hit by this bug upgrading the kernel image to anyone higher than 3.7.
I tried with both 3.8 and 3.9 linux kernel images but it drops into a shell before rootfs gets mounted. I got by this bug adding 'rootdelay=1' option into grub cmdline also.
In a subshell I run ./scripts/local-top/mdadm and then ./scripts/local-top/lvm2 and the LVM volumes got detected properly. To continue the boot process I exited ht shell and the boot process continued fine.