Span containing absolute div positioned incorrectly

[jdm]

<style>
  #infront { top: 0; left: 0; position: absolute; }
</style>
<span>small span
<div id="infront">big div</div>

Firefox:

Servo:

[wusyong]

Looks like pcwalton mentioned this in a FIXME comment:

servo/components/layout/inline.rs

Line 1734 in 6a87180

// FIXME(pcwalton): This will get the absolute containing blocks inside `...` wrong in the

[wusyong]

I think I need some help or pointer because we really can't just remove the arms of match.
Example like this, should remain the same.

Interestingly, layout 2020 can solve this issue. Perhaps there are something wrong when constructing flows?