Using 3.5.300 on 1.12.2 and have set the Open Quests keybind to 'Middle Click', and unbound Pick block, so it is the only thing bound to Middle Click.

After hitting Middle Click(Mouse 3) nothing happens, the book does not open, but if I press basically any key on my keyboard after pressing Middle Click, it will then open, even if it's a key to open another UI interface, like the inventory, it will still just open the quest book.