Contra Proferentem And Ambiguity Preclude Subrogation Recovery

Here's a typical scenario.  The general contractor or owner takes out a all-risk builder's policy to cover a construction project.  Subcontractors are included as additional insureds where required by their subcontracts, but only "as their respective interests may appear."  The policy has a subrogation clause, but the clause includes a provision precluding subrogation against additional insureds. A loss occurs to the property allegedly caused by the sole negligence of a subcontractor.  The insurer pays the loss and brings a subrogation action against the subcontractor.  The subcontractor claims that the insurer has no right of subrogation.  Who prevails?  As in many cases, the answer depends on the jurisdiction.