box.BoxShape.BoxState.Material = new MaterialProperties("foo", 0.98f, 0.5f, 0.5f);
box.BoxShape.BoxState.Material.Advanced = new MaterialAdvancedProperties();
box.BoxShape.BoxState.Material.Advanced.RestitutionCombineMode = CoefficientsCombineMode.Max;
The Ageia docs have the following to say about restitution:
Note: Restitution values near to 1 may cause increasing energy in bounces, depending on the restitution combine mode of the materials. It is therefore recommended that you take care to avoid combined restitution values near 1, at least in cases where the participants are supposed to be able to come to rest touching each other.
So apparently they have defined this as expected behavior and not a bug (although it is fun to watch).
-Kyle
