I'm experiencing a similar problem with a different configuration. The system hangs sometime after entering the key in a normal boot. If I perform a recovery boot it appears to hang because the key prompt is on tty7. Another oddity is that as I enter the key, it seems like a newline gets printed after each keystroke which causes a new prompt line to appear although it still accepts the key.
I'm experiencing a similar problem with a different configuration. The system hangs sometime after entering the key in a normal boot. If I perform a recovery boot it appears to hang because the key prompt is on tty7. Another oddity is that as I enter the key, it seems like a newline gets printed after each keystroke which causes a new prompt line to appear although it still accepts the key.