Check box in scroll box

Does anyone know why a check box (toggle button) won’t work in a scroll box either with or without a size box or scale box?
In that the button just shrinks away to a tiny box (ironically) or a slither of a button that it used to be (see attached screenshot - button is the line at the top)

I have managed to get around it by adding a Canvas Panel to the vertical scroll box, but that still doesn’t explain the above.