Chrome Version       : 50.0.2661.94 m
URLs (if applicable) :
Other browsers tested:
  Add OK or FAIL, along with the version, after other browsers where you
have tested this issue:
     Safari:
    Firefox: OK, 46
         IE: OK, 11

What steps will reproduce the problem?
(1) Open the html file
(2) Click on the background, a popup will appear. It should be centered, but is not.
(3) Press tab to change focus. Now the popup is centered as expected.

What is the expected result?
The popup should be centered from the start.

What happens instead?
At popup creation the popup is horizontally aligned to the left.
This bug corrects itself once the focus changes to something inside of it (like a button).

Please provide any additional information below. Attach a screenshot if
possible.

This worked fine with Chrome 49.
This is connected to the overflow auto. When you set it to scroll or hidden the problem disappears.
 

Deleted: test.html 763 bytes

test.html 763 bytes View Download