ramfs is not visible in the output of 'df'

Issue

ramfs is not displayed in the 'df' output:

[root@system ~]# df -h
Filesystem Size Used Avail Use% Mounted on

/dev/mapper/myvg-rootvol   19G 1.7G 16G 10% /
/dev/sda1                  194M 20M 165M 11% /boot
tmpfs                      502M 0 502M 0% /dev/shm
/dev/mapper/vg_test-test   2.0G 68M 1.9G 4% /app/test

However, it is displayed when the mountpoint is specified:

[root@system ~]# df -h /app/test/ramfs
Filesystem Size Used Avail Use% Mounted on
ramfs 0 0 0 - /app/test/ramfs

Is this behavior expected?