timestamp incorrect over ftp
 

On three Debian servers, two are etch(Dell 2600,2900) and one is sarge(Gateway, circa 2000), when files are accessed over an ftp connection the timestamp shows 00:00 for files older than about 6 months.
On newer files the timestamp shows the correct date/time for the file, but on older files only the date is shown correctly, time is always 00:00.
I changed one server to UTC=yes in etc/default/rcS and rebooted - no change. I changed the ftp server from proftpd to vsftpd - no change. On another I ran tzconfig - no change.
Any suggestions?
Thanks

Is the time on the server correct and in sync with the other servers ?

The time is set by ntp.
With an http directory listing the date/time is correct.
Accessing by ftp with a Gnome or Windows desktop doesn't make any difference.
I even put the servers on different networks (different routers, switches, domains...), no difference.
Thanks