Customize: Tab: Open In (I think “in” would be better): New Window.
Type text in a tab.
Run: EmEditor /ca (or /car, /sca)
It prompts for saving.
Cancel.
Save the files.
Run: EmEditor /ca (or /car, /sca)
The windows closed.
** But the process is still running, till I (run and) exit EmEdTray.
If the Tab setting is [Open in: New Tab in Most Recent Window],
** A new tab will be open before the prompt.
(So the above result won’t happen.)