I can confirm the behavior seems to match what @farrol states—note that it doesn’t seem to create two windows when you open from Finder (Cmd+O or double-click), but it has like a ‘ghost window’ behind the active tab (named untitled) that you end up having to close after you close the document you just opened.
This has been bugging the heck out of me lately, enough to come here and post this animated gif of exactly the issue.
My current preferences file is here: https://github.com/geerlingguy/mac-dev-playbook/blob/master/files/sublime/Preferences.sublime-settings
I have both:
"close_windows_when_empty": true, "create_window_at_startup": false,
And I’m running build 4121 on macOS 11.6.
Here’s the gif:
In the first example, I double-click to open the file, then click the close icon on the tab. An untitled window is left in place that I also have to close.
In the second example, I double-click to open the file, then press Command-W to close the file. An untitled window is left in place that I also have to close.