I always get a message about an already existing file ("File '$NEW_FILENAME' already exists. Overwrite?") when renaming a file, which is followed by the message "Invalid access to memory".
However, the file is actually renamed.
I am using WinSCP 4.3.9 under wine-1.5.10-174-gf881dcf.
I am using sftp to access the server.
Both the server and the client are using Debian GNU/Linux Squeeze (with wine build from git).