With Lubuntu 14.10 and Radeon same problem. Work around by deleting the splash option in the Grub command line.
Edit /etc/default/grub Change: #GRUB_CMDLINE_LINUX_DEFAULT="quiet splash" GRUB_CMDLINE_LINUX_DEFAULT="quiet"
Now an old fashion text message appears and the passphrase can be entered.
With Lubuntu 14.10 and Radeon same problem. Work around by deleting the splash option in the Grub command line.
Edit /etc/default/grub LINUX_DEFAULT= "quiet splash" LINUX_DEFAULT= "quiet"
Change:
#GRUB_CMDLINE_
GRUB_CMDLINE_
Now an old fashion text message appears and the passphrase can be entered.