TreeModel: removing items will make the expand/collapse button vanish

hi,

i have a treemodel which is actually working fine, except removing.
how it looks like:

Code:

---

HEADLINE (expanded view)
 group1
   item1
   item2
   item3
 group2
   itemA
   itemB

---

Code:

---

HEADLINE (collapsed view group1)
 group1
 group2
   itemA
   itemB

---

adding is working fine.
removing items from any expanded group does work fine.

BUT if "group1" is collapsed and i remove an item (eg: "item3"), then the button infront of "group1" will vanish.
i can still press that invisible button to expand "group1".
when i add another item to "group1" the button will appear BUT only if it is expanded.

other groups are not affected until i remove item out of them

Code:

---

bool TreeModel::insertRows( int row , int count , const QModelIndex &parent )
{
	TreeItem *parentItem = getItem(parent);
	beginInsertRows(parent, row, row + count - 1);
	parentItem->appendChild(tmpItem);
	endInsertRows();
	return true;
}
bool TreeModel::removeRows( int row , int count , const QModelIndex &parent )
{
	TreeItem *parentItem = getItem(parent);
	beginRemoveRows(parent, row, row + count - 1);
	parentItem->removeChild(tmpItem);
	endRemoveRows();
	return true;
}

---

any help or ideas ?

btw:
just tested it with linux and there it is working fine. the button is a rectangle with a cross inside
i am using win7 and the button is a triangle.