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Sometimes a conflict occurs when one cascade results in a delete and another in a save. For example a compositie structure is deleted and the cascade deletes all child-structures. But one of these structures is still in the branchfeatures collection of a branch. The branch cascade insists on the object being saved (or at least not deleted) and the CS cascade wants to delete. Hence a conflict. This can be fixed by removing the structure from both lists or downgrading/removing one of the cascades. In this case the branch should be responsible for saving the features and the CS should have a list of child structures without cascades.
A quick recap of the different cascades :
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A note about orphan cascade:
Orphan only looks at one instance at a time. So a composite structure might have a list of child structures. When a child structure is removed from the CS it is considered an orphan. NHibernate does not care about other relation the structure might have (for example with branch or a new CS)
About reparenting : http://fabiomaulo.blogspot.com/2009/09/nhibernate-tree-re-parenting.html