I have added this bug to the tracker:
https://winscp.net/tracker/1985

Confirming I have the same issue too, the automatic upload doesn't seem to happen when I edit a file opened from a remote server

Thanks for your report.
I have sent you an email with a debug version of WinSCP to the address you have used to register on this forum.

After update I've lost the ability to save (and upload) changed files to remote servers.

How to:
connect to remote server
press "Edit" on any file (your preffered editor will open[sublime for me])
edit anything
press save

expected effect -> changed file will get uploaded to the server
actual effect - nothing happens (file gets saved in tmp location)