Recovery HD mounts on startup
this hint suggests

asr adjust --target /dev/disk0s3 -settype "Apple_Boot"

P.S. use diskutil list to confirm that your "Recovery HD" is disk0s3: it should show like this:

$ diskutil list

/dev/disk0
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *500.3 GB   disk0
   1:                        EFI                         209.7 MB   disk0s1
   2:                  Apple_HFS Macintosh HD            499.4 GB   disk0s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3