QML plasmoid, pageStack.pop() doesn't work

[Gao Xiang]

The sample qml is easy:
======================================================
import QtQuick 1.1
import org.kde.plasma.components 0.1 as PlasmaComponents
Item {
	PlasmaComponents.PageStack {
		id: pageStack
		anchors.fill: parent
		initialPage: [ c, b, a ]
	}
	PlasmaComponents.Page {
		id: a
		anchors.fill: parent
		PlasmaComponents.Label{ text: "a" }
		onStatusChanged: if(status==PlasmaComponents.PageStatus.Active) 
pageStack.pop();
	}
	PlasmaComponents.Page {
		id: b
		anchors.fill: parent
		PlasmaComponents.Label{ text: "b" }
		onStatusChanged: if(status==PlasmaComponents.PageStatus.Active) 
pageStack.pop();
	}	
	PlasmaComponents.Page {
		id: c
		anchors.fill: parent
		PlasmaComponents.Label{ text: "c" }
	}
}
======================================================
I wish to get a "c" in screen.  But I got a "b".  What's wrong?  Why the 
second pageStack.pop() doesn't work?

Thanks.