The scrollbar-gutter spec states that the value of this property is inherited.
So, when a container uses e.g. scrollbar-gutter: always force; to reserve space for the scrollbar, then all of its children will also reserve the same amount of space inside their respective boxes.
This behaviour is likely to break the layout and doesn't seem to be what the author intended.
Proposal: update the scrollbar-gutter spec with Inherited: no.