Comment 47 for bug 508848

Thanks Stefan.

Ubuntu will never mount a filesystem with multiple signatures, since it cannot know which is correct and getting it wrong could badly corrupt the filesystem. You'll need to use wipefs to remove the signature that is incorrect.

I'd recommend backing up the device first, you probably only need the first megabyte at most, try:

  # dd if=/dev/mapper/var of=var.bak bs=1M count=1

Then

  # wipefs -o 0x438

After that, blkid -p /dev/mapper/var should only return the btrfs data and the drive should be mounted