Comment 7 for bug 628400

If anything, I think this is probably a bug in initramfs-tools, a new Debian version of which was merged into maverick for the first time in a long while. Note that plymouth still isn't included in the initramfs by default, so shouldn't be hiding anything; though it is possible that grub itself may be hiding it, I think it's at least as likely that the initramfs-tools hooks no longer work as expected.

So I would suggest testing by downgrading initramfs-tools and regenerating the initramfs to see if it's reproducible, and if it still is, then we're probably looking at an interaction between current grub2 behavior and initramfs-tools.