Comment 2 for bug 1296488

Thanks TJ Saunders, follow is his reply:

Here's your culprit here. By default, proftpd does not allow overwriting
of existing files (this includes appending to existing files); see:

  http://www.proftpd.org/docs/directives/linked/config_ref_AllowOverwrite.html

This means that adding e.g.:

  <Global>
    AllowOverwrite on
  </Global>

to your proftpd.conf should help.

And it's works.