Comment 5 for bug 537849

Comparison Between Ubuntu 10.04 and 11.04
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Ubuntu 11 exhibits the same behavior as Ubuntu 10. However... a potential workaround may have been found for Ubuntu 11 as it appears to be working... Enable motherboard redirection
  -- (ENABLED, com1, vt100, 115200, redirect after console *****DISABLED*****) appears to fix the issues

Grub2 Config
-------------------
GRUB_DEFAULT=0
GRUB_HIDDEN_TIMEOUT=5
GRUB_HIDDEN_TIMEOUT_QUIET=false
GRUB_TIMEOUT=10
GRUB_DISTRIBUTOR=`lsb_release -i -s 2> /dev/null || echo Debian`
GRUB_CMDLINE_LINUX_DEFAULT="quiet"
GRUB_CMDLINE_LINUX="console=tty0 console=ttyS0,115200n8"
GRUB_TERMINAL="serial console"
GRUB_SERIAL_COMMAND="serial --speed=115200 --unit=0 --word=8 --parity=no --stop=1"

Observed Effects in Ubuntu 11.04
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- Disable motherboard console redirection (DISABLED, com1, vt100, 115200, redirect after console DISABLED)
-- no motherboard serial access
-- serial console shift key *does not* work to display menu
-- serial console tapping ESC multiple times quickly will allow menu to be displayed

- Enable motherboard redirection (ENABLED, com1, vt100, 115200, redirect after console ENABLED)
-- yes / motherboard serial access
-- error message(s) appears error: unknown command `terminal'.
-- serial console shift key *does not* work
-- serial console tapping ESC multiple times flickers the menu for one second then it disappears

- ENABLED, com1, vt100, 115200, redirect after console *****DISABLED*****
-- yes / motherboard serial access
-- serial console shift key *does not* work to display menu
-- serial console tapping ESC multiple times quickly will allow menu to be displayed

I will be testing Ubuntu 10.04 again to see if the above solution works. For the record... Ubuntu 8 worked with - Enable motherboard redirection (ENABLED, com1, vt100, 115200, redirect after console ENABLED) settings