For anyone who suffers from the same reason and doesn't want to wait for the next release: change -a to two spaces using hex editor at byte 34CE52 in winscp.exe. It works.
BTW: I like WinSCP very much. It is very convenient, especially for people preferring keyboard to mouse (like me).
BTW: I like WinSCP very much. It is very convenient, especially for people preferring keyboard to mouse (like me).