Overflow-scroll in Modal will swipe full app out of viewport

ionic-v1
1

I have a modal like that:

ion-modal-view
  ion-header
  ion-content(overflow-scroll='true')
    // some content

When I scroll to the end and keep swipe up, the full app swiped(or dragged?) out of viewport from top. This issue happend on emulator(4.1, 4.2), chrome and real device(4.3). If I use ion-content with transform scroll, it’s not happened.

I tried toggle.modal-open pointer-events: none; on chrome (disable and re-enable it), and it sloved this issue. But I dont know why it’s happened ?