See this link for a known interoperability issue with Pure-FTPD:
https://winscp.net/eng/docs/faq_line_breaks#known_issues
Edit 2023: WinSCP 5.18 and newer unchecks that box automatically when you change the editor from Notepad to another:
Issue 1872 – Automatically restore external editor defaults when changing editor command from Notepad to 3rd party editor
https://winscp.net/eng/docs/faq_line_breaks#known_issues
Edit 2023: WinSCP 5.18 and newer unchecks that box automatically when you change the editor from Notepad to another:
Issue 1872 – Automatically restore external editor defaults when changing editor command from Notepad to 3rd party editor