UserAgent: Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/56.0.2924.87 Safari/537.36

Example URL:
http://sinst.html.xdomain.jp/zengaku/jkkn/chrome_bug.html

Steps to reproduce the problem:
1. Use a touch device (such as Android smart phone and Windows-10 touch screen PC)
2. Place HTML tags of the SNS share buttons
3. Apply CSS style of 'position:relative; z-index:1' to the tag
4. Overlay a div element with 'position:fixed; z-index:2' over the share buttons
5. Tap the buttons through the overlay div. (This bug only occurs at the top and bottom edges of the overlay div.)

What is the expected behavior?
The tap to the SNS share button should be blocked by the overlay div.

What went wrong?
Even if the SNS share buttons are totally hidden by the overlay, they behave as if tapped (only when tapped at the top and bottom edges of the overlay div).
The CSS 'z-index' may be ignored in touch actions.

Does it occur on multiple sites: Yes

Is it a problem with a plugin? No 

Did this work before? N/A 

Does this work in other browsers? Yes

Chrome version: 56.0.2924.87  Channel: stable
OS Version: 10.0
Flash Version: Shockwave Flash 24.0 r0

Because this doesn't occur when clicked with mouse, this is not a bug of mouse actions, but a bug of touch actions.

Because the button is rendered correctly ('z-index' works well), this is not a bug of rendering.