The problem I'm having in version 5.7.5 occurs when I select SFTP as the protocol and then set port to be 443. After changing the port, the protocol is automatically changed to WebDAV.
Vice-versa if I try and set port to 443 then change protocol to SFTP. The port changes back to 22.
For the affected sessions I have been able to work around this by deleting the FSProtocol line in the winscp.ini file and ensuring port is set to 443.
This did not seem to occur in previous versions. I think the version update also changed the protocol for my saved sessions to WebDAV when it used to be SFTP, but I can't be sure I didn't quickly edit and save in a rush without noticing the protocol change.
Note: I'm using the portable version of WinSCP from PortableApps.