My guess is that FileZilla may have incorrectly set the LastModification date/time stamp of the files transferred to your NAS with the date/time that it was copied.
Thus, when you run the SyncBack profile, during scan stage, it found that the LastModified date/time values of your NAS files doesn't match with those files on HDD, and proposed to copy them across.
To find out exactly what those differences are, you'll need to perform a run (Ctrl+R) and when the Differences dialog window pops up, select/highlight a file that has been proposed to be copied to Destination (which you know that has already been copied to Destination and no changes were made to the Source file) and look at the lower-left corner for a panel which will show what those differences are.
Screenshot of Differences window:
http://www.2brightsparks.com/syncback/h ... delete.gif
We will not propose to copy Unchanged files @ Destination unless they are found to be different (from Source) during scan stage.
Thus, when you run the SyncBack profile, during scan stage, it found that the LastModified date/time values of your NAS files doesn't match with those files on HDD, and proposed to copy them across.
To find out exactly what those differences are, you'll need to perform a run (Ctrl+R) and when the Differences dialog window pops up, select/highlight a file that has been proposed to be copied to Destination (which you know that has already been copied to Destination and no changes were made to the Source file) and look at the lower-left corner for a panel which will show what those differences are.
Screenshot of Differences window:
http://www.2brightsparks.com/syncback/h ... delete.gif
We will not propose to copy Unchanged files @ Destination unless they are found to be different (from Source) during scan stage.