Coming from filezilla and in filezilla this is default behaviour. After edit-> save remote file filezilla warn overwrite.
I know that FileZilla does that. I find that a strange behavior.
People are actually complaining about that and switch to WinSCP to get rid of the confirmation:
https://trac.filezilla-project.org/ticket/4694
You are the first one who misses the confirmation in WinSCP.