TreeListView item's IsExpanded returns false no matter what

[D]

I want to save the expansion state of my TreeListView before I reload the data and I use the following code:

foreach (var item in _currentTreeListView.Items)
{
    if (_currentTreeListView.IsExpanded(item))
    {
        expandedItems.Add(item);
    }
}

// Data update and TreeListView reload

foreach (var item in expandedItems)
{
    _currentTreeListView.ExpandHierarchyItem(item);
}

But _currentTreeListView.IsExpanded(item) returns false no matter if the corresponding item is expanded in the TreeListView. What's the problem?