Try updating to the last development build, i don't know if 973.1 has the bug but i have made 3 files of 1.5, 3 and 6 GB and don't see a problem with file size.
[00:01:00] RETR edit3.rar
[00:01:00] 150 Opening data connection for edit3.rar (6527999873 bytes).
[00:08:58] 6527999873 bytes received successfully. (13336.82 KB/s) (00:07:58).
[00:08:59] 226 Transfer ok
![Image](http://aok.smartftp.com/smartftp-huge-files.png)