Well, it's probably because the first instance is not initialized yet, when the second is starting, so the second does not detect that the first is running already. There's hardly anything that we can do about this.

Of course except for using single command to open all files at once. But that would require yet another configuration option, as not all editors allow this.

Opening multiple remote files with 5.7.7 to edit in Atom results in multiple Windows to open(regardless of it being run via update.exe, atom.cmd or the latest Atom.exe 1.10.0 , although "External editor opens each file in separate window (process)" is not selected.

It does work when opening the files separately.

Also see https://superuser.com/questions/930136/how-to-set-up-atom-io-as-a-winscp-external-editor#comment1602090_930137

It would be nice to have a solution and mention on https://winscp.net/eng/docs/integration_editor

Thanks!