[css-overflow-3] Link to issue

Author: frivoal

css-overflow-3/Overview.bs

@@ -220,7 +220,7 @@ Scrollable Overflow</h3>
 			coincide with the end edges of its content area
 			when scrolled to the end.
 
-			Issue: It's not yet clear if including the end-side padding in the scrollable layer is Web-compatible, so this clause is under investigation.
+			Issue(129): It's not yet clear if including the end-side padding in the scrollable layer is Web-compatible, so this clause is under investigation.
 			It appears that Chrome and Safari include such padding <a href="https://bug748518.bmoattachments.org/attachment.cgi?id=618078">in the block axis</a>;
 			and the behavior in the inline axis is <a href="http://jsbin.com/digadoyohi/1/edit?html,css,output">not</a> <a href="http://jsbin.com/vexahocayi/1/edit?html,css,output">clear</a>.