It is not a bug. It's a suboptimal definition in css standard.
If you use a list like ul, ol with default value for list-style-position (outside), you will get what you see (more or less).
CSS 2.1 standard:
The marker box is outside the principal block box. CSS 2.1 does not specify the precise location of the marker box or its position in the painting order, but does require that for list items whose 'direction' property is 'ltr' the marker box be on the left side of the content and for elements whose 'direction' property is 'rtl' the marker box be on the right side of the content.
I don't think, that kobo will change the behavior of the user agent. But you can put a left margin in.
ol.sgc-4 {list-style: upper-roman; margin-left: 16px}