Overriding data() in subclass of QStandardItem makes setFlags() not working

QVariant CollectionItem::data(int role) const
{
 switch(role)
 {
  /*
custom roles
*/
 
  default:
   return QVariant();
 }
}
{quote}
I've encountered this bug:
{quote}
CollectionItem* item = new CollectionItem("Your collection is empty! Visit settings", "", "", 0, false);
qDebug() << item->flags();
 item->setFlags(0);
 qDebug() << item->flags();
 appendRow(item);
 
 QStandardItem *i = new QStandardItem();
 qDebug() << i->flags();
 i->setFlags(0);
 qDebug() << i->flags();

QFlags(0x1|0x2|0x4|0x8|0x20)
QFlags(0x1|0x2|0x4|0x8|0x20)
QFlags(0x1|0x2|0x4|0x8|0x20)
QFlags()

default:
    return QStandardItem::data(role);