[Webkit-unassigned] [Bug 176053] New: dynamically added position absolute element inside position fixed element is rendered in wrong place

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=176053

            Bug ID: 176053
           Summary: dynamically added position absolute element inside
                    position fixed element is rendered in wrong place
           Product: WebKit
           Version: Safari Technology Preview
          Hardware: iPhone / iPad
                OS: iOS 11
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: CSS
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: wart.claes at gmail.com

Created attachment 319253

  --> https://bugs.webkit.org/attachment.cgi?id=319253&action=review

test case

When dynamically placing an element with position: absolute inside an position: fixed element renders in the wrong place.

This has been tested in:
- iPhone 7+: iOS 11 public beta 7:  incorrect
- iPhone 7:  iOS 10.3.3:            correct
- iPhone 7+: iOS 10.2:              correct

## Steps to reproduce:
1) Open attached test case
2) Scroll down
3) Click button

## Expected result
A pink block should be shown on top of the button.

## iOS 11 result
The pink block is positioned to high on the page.

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