SwingWorker problem

Sometime,when I add new contact,the reply packet return a little delay.So the swingworker’s finish method call get() which return null then will report a cannot add contact error message dialog.But exactly the contact is added.

The attached file is the packet details.
packet.txt.zip (456 Bytes)

BTW,I found if I use the official released spark version,it works fine.But if I use our custom spark version,the packet will delay.And use the same openfire server. We just redesign the ui,but not change with the RosterDialog.

Anybody could give me some suggetion to advoid that?