When mounted from file storage and using /dev/urandom for key, passphrase is still asked at boot time when more than 1 entry in /etc/crypttab

OS: Ubuntu 16.04.3 64bit, all latest updates applied.

Setup:

# dd if=/dev/urandom of=/var/cswap bs=1M count=128
128+0 records in
128+0 records out
134217728 bytes (134 MB, 128 MiB) copied, 9.85457 s, 13.6 MB/s
# dd if=/dev/urandom of=/var/ctmp bs=1M count=128
128+0 records in
128+0 records out
134217728 bytes (134 MB, 128 MiB) copied, 9.43066 s, 14.2 MB/s
# chmod 600 /var/cswap /var/ctmp

Setup 1:

/etc/crypttab:
cswap /var/cswap /dev/urandom swap,cipher=aes-xts-plain64

/etc/fstab:
/dev/mapper/cswap none swap sw,nofail 0 0

System boots normally, cswap is initialzed and encrypted swap is mounted.

Setup 2:
/etc/crypttab:
cswap /var/cswap /dev/urandom swap,cipher=aes-xts-plain64
ctmp /var/ctmp /dev/urandom tmp

/etc/fstab:
/dev/mapper/cswap none swap sw,nofail 0 0
/dev/mapper/ctmp /tmp ext4 defaults,noatime,nodiratime,nosuid,nofail 0 2

When booting, the below is asked at init screen (on console):
"Please enter passphrase for disk cswap on none!"
(will not proceed with boot sequence until answered)

After Enter is pressed, system boots up, both cswap and ctmp are initialized and mounted.