The current functionality DOES highlight the ACTIVE COST CATEGORY under the CURRENT PHASE.  The Treeview does not allow for highlighting at 2 different levels (i.e. Phase and Cost Category).

So best work around is to colapse the PHASE that is not currently in used IF the trieeview contains too many phases/costcategories, so that the current PHASE is always visible (and the categories under that Phase is highlighted).