Weird Safari scroll bleed bug

What feature in safari would do this?

My first section (z-index 1) is animated and with 3 stickies. The second one (z-index 2) is just static . Anyway the animated images are flicking through the second section. They do it the first time BUT not the second???!!! And even more weird this happens only in this very wide aspect ratio. If I change the browser window to more higher. This does not happen!!??

Bug shown here:

Link here:

Here is my site Read-Only: LINK
(how to share your site Read-Only link)

I made a really cheap fix. Just added a blue div to the bottom of the first section it coming/down over with minus bottom margin.

Would be still nice to know why this happens in safari…