problem about "nodeHitAt"

[ma zhenduo]

There are some problem about "nodeHitAt".  When the filter ( <filter id="f1"><feOffset dx="50" dy="50" /></filter>) is appled on the shape     ( <circle cx="85"  cy="135" r="50" filter="url(#f1)" />),     I can't find it by calling "nodeHitAt(rootGraphicsNode)".     But another filter         ( <filter id="f1"><feSpecularLighting in="FillPaint" in2="SourceAlpha" lighting-color="blue" result="specOut">                 <fePointLight/>           </feSpecularLighting>            <feComposite in="specOut" in2="SourceAlpha" operator="in" result="specOut"/>filter>         ) is no problem.   thanks in advance.