Check out fast/events/offsetX-offsetY.html and move the column block over the fixed positioned element. Everything paints behind the fixed positioned element when the foreground text should paint on top of it.
I don't think this blocks turning new multicolumn on, but it *will* be important to fix.
Created attachment 230530 [details]
Test case. Note that repainting (e.g., selection) is broken too.
This is fixed by changing the layer for the flow thread to be normal flow only but still make it be self-painting.
Created attachment 230551 [details]
Comment on attachment 230551 [details]
View in context: https://bugs.webkit.org/attachment.cgi?id=230551&action=review
> + || renderer().isInFlowRenderFlowThread())
Can you indent this line or unwrap it.
Fixed in r168076.
This change broke fast/multicol/fixed-stack.html:
More precisely, this new test fails on all WK2 testers.