Actually define how to position once you find the static position.

Author: tabatkins

css3-flexbox/Overview.html

@@ -1056,6 +1056,23 @@ <h3 id=abspos-items><span class=secno>4.1. </span> Absolutely-Positioned
    href="#flex-item-static-position"><i>static position</i></a> is the
    <i>cross-start edge</i> of the first <i>flex line</i>.
 
+  <p> If both ‘<code class=property>left</code>’ and ‘<code
+   class=property>right</code>’ are ‘<a href="#align-self-auto"><code
+   class=css>auto</code></a>’, the <a href="#flex-item"><i>flex
+   item</i></a> must be positioned so that its <a
+   href="#main-start"><i>main-start</i></a> or <a
+   href="#cross-start"><i>cross-start</i></a> edge (whichever is in the
+   horizontal axis) is aligned with the <a
+   href="#flex-item-static-position"><i>static position</i></a>. If both
+   ‘<code class=property>top</code>’ and ‘<code
+   class=property>bottom</code>’ are ‘<a href="#align-self-auto"><code
+   class=css>auto</code></a>’, the <a href="#flex-item"><i>flex
+   item</i></a> must be positioned so that its <a
+   href="#main-start"><i>main-start</i></a> or <a
+   href="#cross-start"><i>cross-start</i></a> edge (whichever is in the
+   vertical axis) is aligned with the <a
+   href="#flex-item-static-position"><i>static position</i></a>.
+
   <p class=note> These rules are intended to more-or-less match what the
    position would be if the abspos was a 0x0 in-flow flex item that
    participated in flex layout.

css3-flexbox/Overview.src.html

@@ -705,6 +705,19 @@ <h3 id='abspos-items'>
 		that item is in.
 		Otherwise, the <i>static position</i> is the <i>cross-start edge</i> of the first <i>flex line</i>.
 
+	<p>
+		If both 'left' and 'right' are ''auto'',
+		the <i>flex item</i> must be positioned so that
+		its <i>main-start</i> or <i>cross-start</i> edge
+		(whichever is in the horizontal axis)
+		is aligned with the <i>static position</i>.
+		If both 'top' and 'bottom' are ''auto'',
+		the <i>flex item</i> must be positioned so that
+		its <i>main-start</i> or <i>cross-start</i> edge
+		(whichever is in the vertical axis)
+		is aligned with the <i>static position</i>.
+
+
 	<p class='note'>
 		These rules are intended to more-or-less match
 		what the position would be if the abspos was a 0x0 in-flow flex item