5.2.5 Internal editor issue

It looks like UTF-8 BOM.
I suppose you have set UTF-8 encoding as default for internal editor, right?

You can configure WinSCP to drop the BOM on upload (Remove BOM and EOF marks option):
https://winscp.net/eng/docs/ui_transfer_custom

This issue has been added to the tracker:
https://winscp.net/tracker/1081