I understand that according to the SFTP specs (https://tools.ietf.org/html/draft-ietf-secsh-filexfer-13#page-21), the "mtime" field is supposed to be expressed in "Unix time." It seems that the WinSCP .NET component is not correctly converting the NTFS timestamp into this format. It may just be grabbing certain bits directly from the NTPS timestamp and populating the "mtime" field with that, and the server on the receiving end is then interpreting this timestamp (as it should!) as a number of seconds since the Unix epoch.
Any insight or suggestions for a workaround would be greatly appreciated.