When you have multiple backgrounds on a region, using insets. Then add a border. You expect the backgrounds to be inside that border not the border drawn over the top of those backgrounds which is what happens today. So what we need to do is add the combined border width on the inside of the bounds to all back ground insets.

Eg if there is a 10px internal stroked border and a background with inset 1px. The backgrounds inset should be 11px;

Eg if there is a 6px centered stroked border and a background with inset 1px. The backgrounds inset should be 4px = ((6/2)+1);