I just tried changing two settings (at once), and one or both of them fixed the problem. Hopefully this will help with troubleshooting.
Under Options > Note, "Create new note in a new window" was unchecked (although it was checked before the update), and "Set new note focus to title" was checked (as it was before the update).
Just now, I checked "Create new note in a new window" and unchecked "Set new note focus to title". So now when I'm typing in a note with its own window, the cursor does not keep jumping back to the subject.
