Tr:tree expansion state is lost

["Meyer, Stefan" <S....@S2neueinformatik.de>]

I use a tree with commandLinks in the nodeStamp. When clickng on an
expanded link the action is executed as expected but the link is
collapsed. The action in the commandLink points to the same viewId. If I
return null instead of the outcome leading to the same view id it works.
How do I keep the expansion state for different views with the same
tree?
I basically want the disclosedRowKeys to be persisted in pageFlowScope,
so that in every browser window I have a consistent treestate for
different views. Is that possible?