A bit of feedback as I found a workaround for this issue.

The root cause seems pretty hairy but related to the way osx/efi pairs early
with bluetooth devices and present them as USB devices during boot.

For a long time I had to follow a rather involved (but working !) boot
process:

- boot OSX
- reboot
- hold the 'Alt' key to trigger rEFIt (which is where the warm restart is 
required)
- select linux
- at the grub prompt, select the right kernel

This stopped working when I reported this bug.

I then went into porting the bluetooth link keys from osx to ubuntu and this
did the trick.

My suspicion is therefore that something changed in the kernel regarding the
bt devices handling or its relationship with presenting the bt devices as
USB ones and using the right link keys allows the kernel to reconnect them
properly.

For the record, the way to migrate the link keys from osx to ubuntu goes
like (providing you plug some keyboard/mouse to do it :-}):

1) Pair the bt devices in OSX

2) Get their link keys in
  /media/osx/private/var/root/Library/Preferences/blued.plist.

The osx partition needs to be mounted under Ubuntu for this to work.

3) Decipher with:

  $ plutil /media/osx/private/var/root/Library/Preferences/blued.plist

'plutil' is provided by the libplist-utils package

4) For each key:

   $ echo <data> | base64 -d | hexdump -C

The bytes are stored (hence displayed) in the reversed order of the one
expected in linkkeys (just don't ask me why, I bang my head in despair when
I found this dirty trick).

i.e. ff d4 7b db 3d be 35 7c 9f 9a b4 f1 7f 51 3e 1f
becomes 1F3E517FF1B49A9F7C35BE3DDB7BD4Ff

5) Put the link keys obtained above in the expected files:

 /var/lib/bluetooth/<MAC address>/linkkeys

With that in place, while I still need to have OSX/rEFIt/grub see my
keyboard (which still requires a double boot dance), both the mouse and the
keyboard are available at the lightdm stage \o/


In other words the working boot sequence is now:

- boot OSX
- reboot
- hold the 'Alt' key to trigger rEFIt (warm restart still required)
- select linux

And I can safely let grub select the default kernel.

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https://bugs.launchpad.net/bugs/877539

Title:
  bt keyboard and magic mouse lost when using 3.0.0.12.14

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