I'm pretty particular about the order in which my modifier buttons are laid out, for workflow reasons. When you're configuring your modifier sets, if you try to empty out a specific button so you can put a specific modifier in it, that button just keeps getting auto-filled with other modifiers you already have assigned to other buttons.
In the below example, I move the Smooth modifier down and to the left, then I want to empty the button to the right of it so I can place the Push modifier there, but every time I try to empty that button something else jumps into it.
