it looks strange. I've tried to reproduce it by following code and received a clean upload with no appended digits. Could you please try similar code on your place?
Sftp sftp = new Sftp();
// list files on remote directory
SftpItemCollection items = sftp.GetList();
foreach (SftpItem item in items)
It produced following output:
If the problem persists could you please create a communication log file as described at http://www.rebex.net/kb/logging.aspx and either edit your question to include the log or send it to firstname.lastname@example.org for analysis?