Take this markup, stick it in an html file, and view it in mobile Safari on an iPad. I'm using an iPad Mini 4 on iOS 9.3.2.
<html lang="en">
<head>
<title>long</title>
<meta name="viewport" content="width=device-width, initial-scale=1.0, minimum-scale=1.0, maximum-scale=1.0, user-scalable=no">
<meta name="apple-mobile-web-app-capable" content="yes">
</head>
<body style="background-color: #112FCB">
<div id="viewport" style="height: 928px; width: 768px; margin-top: 0px; display: block;">
<div style="width: 638.3376623376623px; height: 771.3246753246754px; transform: scale(1.203125, 1.203125); background-position-x: 0px;">
<div class="page-container" style="width: 100%; height: 100%; overflow-y: scroll; overflow-x: hidden; -webkit-overflow-scrolling: touch; position: relative;">
<div class="page-scroll" style="height: 10202px; width: 640px; left: 0px; top: 0px;">
<div style="position: absolute; left: 254px; top: 259px; width: 88px; height: 89px; display: block; background-color: rgb(255, 255, 255);">
<span style="top:-3px;left:0px;">1</span>
</div>
<div style="position: absolute; left: 252px; top: 1098px; width: 113px; height: 60px; display: block; overflow: visible; background-color: rgb(255, 255, 255);">`
<span style="top:-3px;left:0px;">2</span>
</div>
<div style="position: absolute; left: 229px; top: 1821px; width: 88px; height: 89px; display: block; overflow: visible; background-color: rgb(255, 255, 255);">
<span style="top:-3px;left:0px;">3</span>
</div>
<div style="position: absolute; left: 253px; top: 2503px; width: 88px; height: 89px; display: block; overflow: visible; background-color: rgb(255, 255, 255);">
<span style="top:-3px;left:0px;">4</span>
</div>
</div>
</div>
</div>
</div>
</body>
</html>
So basically we have 4 absolutely positioned divs for showing where you are on the page, inside a very tall div (.page-scroll), which is inside a relatively positioned div with overflow-y: scroll and -webkit-overflow-scrolling: touch (.page-container). The other parent divs (page-viewport and viewport) are there to ensure a consistent look across devices.
On every other device we've tried, swiping to scroll scrolls the page-scroll div inside the page-container div as expected. However, on iPad, we are seeing non-deterministic behavior. If you swipe quickly, the page scrolls normally, but if you swipe slowly, the page will sometimes rubberband. It's as if the touchstart event is getting sent to one of the parent divs, and so the iPad thinks it is at the bottom or top of the page.
However! If -webkit-overflow-scrolling: touch is removed from the .page-container div, the problem disappears. But you lose momentum scrolling, which sucks. I should also note that if this markup is loaded onto a page via an iframe, the problem goes away, but that is not really an option for us (because reasons).
I have tried the suggestion in this similar question to put yet another div inside .page-scroll and set height: calc(100% + 1px), but that did not fix the bug.
I do see a lot of related questions that indicate -webkit-overflow-scrolling: touch has a myriad of problems, but none of those questions are quite exactly this bug, I think.
Has anyone encountered this before? Any suggestions for workarounds?
