There appears to be a bug in ProFTPD version 1.2.5 and RC versions, the bug exists in the login process of the daemon. Specifically in the password authentication. After the client has connected to the remote host and sends the login username whether be a legit or anonymous, if the user then issues the "PASS" command with 12 Kilobytes of data or more as the password, the daemon will crash.
Credit:
The information has been provided by BuRn-X.