[Webkit-unassigned] [Bug 257119] New: onpointerdown event not firing on position: fixed elements at certain scroll position

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=257119

            Bug ID: 257119
           Summary: onpointerdown event not firing on position: fixed
                    elements at certain scroll position
           Product: WebKit
           Version: Safari 16
          Hardware: iPhone / iPad
                OS: Other
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: UI Events
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: shuangqiu2 at gmail.com

Created attachment 466446

  --> https://bugs.webkit.org/attachment.cgi?id=466446&action=review

screen recording of the reproduction

Tapping an element doesn't fire the pointer down event in this setup:
  1. The button itself has "position: fixed" set
  2. The ancestors have "height: 100%" set
  3. The page has a viewport meta tag set (seems to happen only on a small-ish viewport width. If I set the width to 1200, it works testing on an ipad mini)

You could find the reproduction sandbox here: https://codesandbox.io/s/young-moon-4uhybj?file=/public/index.html. 

Attached is a video of my reproduction on an ipad mini with iPadOS 16.3.1: the button has an onpointerdown callback that will update the number on the button. When I scroll to the bottom and scroll back up a bit, tapping doesn't update the value until I scroll to a different position.

It works if I change one of the conditions above, or if I use onclick instead.

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