Describe the bug
When opening an entry, the game tick loop stops (mobs stop movin in the background) and the game saves (can be seen in the log).
That seems a bit excessive.
Interestingly, when looking at a category screen, the game resumes as normal.

To Reproduce

1. Open a book in singleplayer.
2. Repeatedly open/close it and switch from categories to entries
3. Observe the mc log

Expected behavior
The game either stopping time entirely when opening the book, or never (will probably fix the saving automatically)

Hmm interesting. I think GUIs have some overridable function that governs this. I'll experiment!