IFrame lets you scroll down in Safari 9.0.3 OSX

Question

IFrame lets you scroll down in Safari 9.0.3 OSX

For some strange reason, Safari allows me to scroll down using finger gestures inside an iFrame. However, if I use the scroll bar, I can scroll up and down. WTF ?!

This is html and css for the iframe and its shell.

#iframe-wrapper {
  -webkit-overflow-scrolling: touch !important;
  overflow-y: scroll !important;
  height: 312px;
}
#iframe-wrapper>iframe {
  border-radius: 4px;
  background-color: white;
  border: none;
  -webkit-box-shadow: inset 0px 0px 15px -5px rgba(0, 0, 0, 0.75);
  -moz-box-shadow: inset 0px 0px 15px -5px rgba(0, 0, 0, 0.75);
  box-shadow: inset 0px 0px 15px -5px rgba(0, 0, 0, 0.75);
}
.fixed-window {
  position: fixed;
  height: 100%;
  width: 100%;
  overflow-y: auto;
  overflow-x: hidden;
  left: 0;
  right: 0;
}
.popup {
  margin: -100px auto 100px;
  position: absolute;
  border: 0px solid white;
  -webkit-border-radius: 10px;
  -moz-border-radius: 10px;
  border-radius: 10px;
  box-shadow: 0px 0px 18px rgba(0, 0, 0, 0.4);
  max-width: 720px;
  width: 100%;
  top: 50%;
  left: 50%;
  transform: translateX(-50%);
  -ms-transform: translateX(-50%);
  -webkit-transform: translateX(-50%);
}
#container {
  padding: 0 40px;
}

<div class="fixed-window">
  <div class="popup">
    <div id="container">
      <div class="on-submit-hide">
        <div id="iframe-wrapper">
          <iframe height="100%" width="100%" src="http://www.lipsum.com/feed/html">
          </iframe>
        </div>
      </div>
    </div>
  </div>
</div>