iconview item would change the height after update the TreeModel

[Liangxu Wang <wlx mygis org>]

Hi,
I am using Gtk::IconView to display some pdf's thumbnail, and without
any problem. But encounter a strange problem, the iconview item's height
will increase after a model's update if the model's content unchanged. 
For e.g., I use a update() function to do the update thing:

	refListModel->clear();
	for(int i=0;i<t.size();i++)
	{
        Gtk::TreeModel::Row row = *(refListModel->append());
		row[columns.id] = t[i].id;
        row[columns.name] =  t[i].name;
		row[columns.click] =  t[i].click;
		row[columns.uri]=t[i].uri;
		row[columns.pixbuf]=get_pixbuf(t[i].uri);
	}
in this function, if the refListModel's content same as before
refListModel->clear() function, the iconview will get this problem. 
So I don't know, is this problem related with gtkmm or gtk+, and is this
a bug or a feature?
and the screenshot:
 normal one: http://wlx.westgis.ac.cn/iconview-first.png
first update: http://wlx.westgis.ac.cn/iconview-second.png
second update: http://wlx.westgis.ac.cn/iconview-third.png

Any comments are appreciated.

Sincerely yours,
Liangxu Wang