Comment 2 for bug 1225136

What plymouth theme / frontend are you using? I'm able to reproduce an issue like this with plymouth-theme-ubuntu-text: the prompt is shown, but is then almost immediately overwritten when the screen refreshes to show the 'Continue to wait, [...]' message. But if I start typing, it's captured as a passphrase and I'm able to unlock the disk - and all disks are mounted correctly.

So I think this is a bug in the text theme. But I don't see any way that this could be a regression since 13.04, because the text theme hasn't changed since raring. So maybe instead something has changed with your hardware that causes the text splash to be used instead of the graphical splash? Have you recently enabled nvidia/fglrx binary drivers for your system?