Slot/button is automatically selected when opening any JSON screen

Opening JSON screens will autoselect the first slot or button, disregarding the cursor's current position. This is most noticeable on containers such as chests, dispensers and furnaces, but can also be seen in a lot of weirder screens, like the command block and the book and quill or even the game's menus, such as the options screen. If there's an item in the selected slot, the hover text will appear at the cursor's actual position.

There are some exceptions, such as any screens relating to the marketplace and the character creator.