In function handleEvent in Roster.as line 521:
case RosterExtension.NS:
var tempIQ:IQ = eventObj.data;
…
the IQ message is not saved in the data property of eventObj, but in the iq property, as you can verify in the handleIQ function in XMPPConnection.as line 688:
dispatchEvent();
The consequences are when you’'re online your roster is not updated if someone else add or remove you from his own roster.