Non root user gets setsockopt error when running ftp in debug mode (-d) on RHEL6

Issue

Running an ftp script (ftp -dvn < ftp_commands), a non-privileged user gets the following error:

ftp> ls
ftp: setsockopt (ignored): Permission denied

And in an strace:

bind(4, {sa\_family=AF\_INET, sin\_port=htons(0), sin\_addr=inet\_addr("172.21.25.16")}, 128) = 0
setsockopt(4, SOL\_SOCKET, SO\_DEBUG, [1], 4) = -1 EACCES (Permission denied)

When ftp is run as root, there is no error.