UserAgent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/57.0.2987.110 Safari/537.36

Steps to reproduce the problem:
1. Set up a CSS-Grid layout in a container, and also include an element that is position fixed (like a slideshow overlay). 
2. Then Hide the fixed element with javascript (like someone is closing the slideshow to return to the normal layout.

Codepend example:
http://codepen.io/howardelton/full/ZejWdg/

1. click the button to display the overlay.
2. click the overlay to make it disappear (where the error occurs)

What is the expected behavior?
When element is hidden, the layout behind it should remain unaltered, and become fully visible. This is the behaviour in FF 52.

What went wrong?
When the element is hidden, the space where is was turns white and the elements underneath are not redrawn. 

Did this work before? No 

Chrome version: 57.0.2987.110  Channel: stable
OS Version: 10.0
Flash Version: 

If the "position: fixed" element is moved to outside of the Grid container, then it functions as expected. Since this is not required in FF, I think it is a bug.