Inner Stroke not behaving as expected in 6.1

Hello - just started using 6.1, great to see new features rolling out to quickly.

Inner stroke - am I right in expecting this to add a stroke, inside the dimensions of a shape, without going outside of those bounds? If so, I can’t get it to do so!

I have a simple shape as part of a web interface design, a square 100Px, I need a border top and bottom so I chose “Horizontal parallel lines” as the shape, blue background, grey stroke, stroke type inner - no stroke appears on screen.Change back to single stroke, and it appears fine, albeit outside of the bounds of the shape, and annoyingly as it’s a 1px stroke, it’s a half PX out of the bounds of the shape I want.

Please help!