Plasmoid : buttons of the configuration window

[kakashi-sempaii]

Hello,
I'm developing a plasmoid and have some problem with the configuration window 
that appears with a right clic : only the buttons "help", "OK" and "Cancel" 
are enabled, and not the button "default settings".
I have tried the following :
Code: 
parent->setButtons( KDialog::Default | KDialog::Apply | KDialog::Ok | 
KDialog::Cancel );

to add also an "apply" button, but nothing happens (in fact, the button "help" 
disappears).  

Does someone know how to deal with this ?
Thanks !