A lot of people have mentioned that the notebook is broken/unreliable/glitchy in TTS.

Well, none of the devs have bothered to respond, so I finally figured out the parameters of this bug.

Before I describe this, note that when I refer to "notebook session", I'm referring to a specific instance where the notebook is opened, edited or not, and then closed.
And when I refer to "game session", a game session ends when you exit the game - either to the main menu, or by directly loading another mod/game.

Here is how the notebook is broken:

1. If you leave the notebook by hitting your keyboard's ESC key, all of the changes you made during that notebook session will be lost.

2. If you leave the notebook by clicking the "X", then that state of the notebook session will be kept - which includes any prior changes, even if they were ESC-out.

Clarifications and Notes:

1. If you leave the notebook by hitting ESC, you can go back into the notebook during that game session and everything will LOOK like it's there. But unless you edit/add text and X-out, the changes added during the notebook session that was ESC-out will be lost.

2. You can ESC-out as much as you want, as long as you modify something in the notebook and X-out prior to saving and leaving the game session. Even if you type a single letter, backspace to clear it, then X-out - you will preserve all the text previously entered with ESC-out.