Timestamp of files through ftp are different that actual timestamp
Proftpd might be doing a timestamp offset on your system.
Edit your /etc/proftpd.conf file, and add:
to the top of the proftpd.conf file. Save, exit, and restart proftpd.
Some reports mention to add the following code into the top section of your proftpd boot script:
eg: /etc/init.d/proftpd or /usr/local/etc/rc.d/proftpd.
claims to have been fixed in 1.3.0rc5, so use 1.3.0 or higher.
Another report of modifying some code in mod_auth.c and recompiling (no followup on this yet)