blkid does not list all devices at default

[Removed by request]

I'm using Ubuntu 15.04 dev with util-linux 2.25.2-4ubuntu2 and "man blkid" says "When device is specified, tokens from only this device are displayed. It is possible to specify multiple device arguments on the command line. If none is given, all devices which appear in /proc/partitions are shown, if
       they are recognized." but it seems without a device argument blkid does not list all recognized devices listed in /proc/partitions as this example shows (but an additional device not listed in /proc/partitions is shown):

root@ubuntu:~# cat /proc/partitions
major minor #blocks name

   8 0 195360984 sda
   8 1 147125248 sda1
   8 2 31447237 sda2
   8 3 1 sda3
   8 5 16776192 sda5
  11 0 810432 sr0
 252 0 16776192 dm-0
root@ubuntu:~# blkid -c /dev/null
/dev/sda1: UUID="05338ff8-a226-421b-90a4-1dd45199f783" TYPE="ext4" PARTUUID="000aa70d-01"
/dev/sda2: UUID="44645410645406D8" TYPE="ntfs" PARTUUID="000aa70d-02"
/dev/sda5: PARTUUID="000aa70d-05"
/dev/sr0: UUID="2015-03-25-00-53-13-00" LABEL="2015_03_25_01_41" TYPE="iso9660"
/dev/mapper/cryptswap1: UUID="aa266386-4df9-4cfc-b4e8-6eff9b51f4aa" TYPE="swap"
root@ubuntu:~# blkid /dev/sda /dev/sda3 /dev/dm-0
/dev/sda: PTUUID="000aa70d" PTTYPE="dos"
/dev/sda3: PTUUID="29f1e303" PTTYPE="dos" PARTUUID="000aa70d-03"
/dev/dm-0: UUID="aa266386-4df9-4cfc-b4e8-6eff9b51f4aa" TYPE="swap"