It is the correct behaviour.

You use the -f flag, which mean:

-f, --fake: Causes everything to be done except for the actual system call; if it's not obvious, this ``fakes'' mounting the filesystem. This option is useful in conjunction with the -v flag to determine what the mount command is trying to do. It can also be used to add entries for devices that were mounted earlier with the -n option. The -f option checks for an existing record in /etc/mtab and fails when the record already exists (with a regular non- fake mount, this check is done by the kernel).

See also Remount a busy disk to read-only mode.

It is the correct behaviour.

You use the -f flag, which mean:

-f, --fake: Causes everything to be done except for the actual system call; if it's not obvious, this ``fakes'' mounting the filesystem. This option is useful in conjunction with the -v flag to determine what the mount command is trying to do. It can also be used to add entries for devices that were mounted earlier with the -n option. The -f option checks for an existing record in /etc/mtab and fails when the record already exists (with a regular non- fake mount, this check is done by the kernel).

See also Remount a busy disk to read-only mode.