Partial or corrupted uploads detected?

What happens when WinSCP uploads a file but for some weird reason the file did not upload completely or correctly on the server. Will WinSCP detect that? In other words, is there a backward check that all files that have been uploaded are correctly uploaded? Or do you think this will never happen - if so, why?

Depends on reasons of failure and transfer protocol:

• Dropped connection: The partially uploaded files remains in the target directory. With SFTP protocol, you can resume the transfer later.
  
• Data are incorrectly transmitted: I believe that with SSH protocol this would by 99% cause confusion in the encryption and the connection closure by one side.
  
• Data are incorrectly stored on the remote file system (but it was not detected by the server, i.e. strange HDD failure, i.e. not probable): This will not be detected. Only way to check this is to download the file back (nonsense) or use some hashing algorithm. As mentioned already today: Hashing is supported only by SFTP protocol and only as optional extension since version 5. And there is no SFTP server I'm aware of supporting protocol version 5.