iframe issue when sticky used

[gunn-fd]

I added an iframe as one of the rows in the list and set it to be sticky, while the sticky works, the iframe sits on top, making its wrapper z-index: 0 instead of 1 fixed it. But when I start to fast scroll I can see the sticky container iframe showing through when its not rendering.
I also noticed if you use the lists scrollbar, I don't see any gaps/unrendered content but if i scroll fast with the trackpad, i can see lots of gaps. my row content is not complex just a few divs and text