overflow: auto; breaks page-mode

Gave me a lot of headaches, finally figured out why pagemode isn't working for me...

1. Go to [Demo Page](https://akryum.github.io/vue-virtual-scroller/#/recycle)
2. Activate page-mode
3. See that it is working
4. Update HTML: ( `Inspect > Elements > Edit as HTML`)
- FROM: div id="app">
- TO THIS: div id="app" style="position: fixed; overflow: auto;"> // my situation
- OR THIS: div id="app" style="position: absolute; overflow: auto;">
- OR THIS: div id="app" style="overflow: auto;">
5. See that scroller only loads first few items.

I'm reporting this issue hoping for a fix or explanation:
- Use a new property, i.e. scrolling-container:"#app"
- Or how should we apply overflow on page-mode?