Forge 43.2.8
FastWorkbench 1.19.2-7.1.0
Placebo 1.19.2-7.1.7

Set:
B:"Remove Recipe Book Button"=false
in fastbench.cfg.

Create new world. Open inventory with 2x2 crafting grid. Click recipe book button to show recipe book. Close inventory without closing recipe book. Save and Quit.

Set:
B:"Remove Recipe Book Button"=true
in fastbench.cfg.

Reopen world. Open inventory with 2x2 crafting grid. Recipe book is still displayed but recipe book button is hidden.

That's fair. :)

This is... sorta on the "not a bug" line, the config only removes the button, because it's really intrusive to do anything else. If you open the recipe book and disable the button, that's on you.