A portability workaround was applied in version 1.2.9 of the FTP server ProFTPD. As a side-effect, CIDR based
(aaa.bbb.ccc.ddd/NN) ACL entries in "Allow" and "Deny" directives act like
an "AllowAll" directive and so FTP clients are granted access to files and
directories although the server configuration might explicitly deny this.
See this bug
report.