Reference object poppers positioned incorrectly when not added to document root

[Benjamin-Dobell]

CodePen demo

https://codepen.io/anon/pen/MMZwLx

Steps to reproduce the problem

1. Add a popper element to the DOM in any element whose local coordinate space is not the same as client coordinate i.e. Add a popper element somewhere other than the document root.
2. Create a popper positioned using a reference object, as opposed to a reference element.

What is the expected behavior?

Popper to be positioned according to the values returned by the reference object.

What went wrong?

Popper is offset too far to the right and/or down depending on where the popper parent element exists within the page.

Any other comments?

PR incoming.