Comment 6 for bug 1311987

So there's a later commit which adds a command-line option to force use of ramfs:

commit 6e19eded3684dc184181093af3bff2ff440f5b53
Author: Rob Landley <email address hidden>
Date: Wed Sep 11 14:26:13 2013 -0700

    initmpfs: use initramfs if rootfstype= or root= specified

    Command line option rootfstype=ramfs to obtain old initramfs behavior, and
    use ramfs instead of tmpfs for stub when root= defined (for cosmetic
    reasons).

Can you try adding rootfstype=ramfs to the kernel parameters and see if this works? Would you be able to do this for cases where you really need ramfs?