(mesh related) code that works in Unity 3.5 does not work in 4.3

The following code was written in Unity 3.5 and worked back then (and still does in 3.5), but I tested it in Unity 4.3 and it no longer works correctly.

         List<edge> borderedges = new List<edge>();
         List<bool> unique = new List<bool>();
         for (int i = 0; i < edges.Count; i++)
         {
             unique.Add(true);
         }
         for (int edgeIndex = 0; edgeIndex < edges.Count; edgeIndex++)
         {
             if (unique[edgeIndex])
             {
                 for (int i = edgeIndex + 1; i < edges.Count - 1; i++)
                 {
                     if (edges[i].a == edges[edgeIndex].b && edges[i].b == edges[edgeIndex].a)
                     {
                         unique[edgeIndex] = false;
                         unique[i] = false;
                         break;
                     }
                 }
             }
         }
         for (int edgeIndex = 0; edgeIndex < edges.Count; edgeIndex++)
         {
             if (unique[edgeIndex])
                 borderedges.Add(edges[edgeIndex]);
         }

I can't see anything that could be wrong, or anything that could cause it to behave differently in Unity 3.5 than 4.

some info about the code: it's part of a function that looks for border-edges (edges that are each only part of a single triangle). an "Edge" is simply a struct with 2 ints, a and b, which are vertices indices.

I tested it on a simple square (2 triangles), and in 3.5 it correctly says the mesh has:

• 4 vertices

• 2 triangles

• 6 edges

• 4 borderedges

yet in 4.3 it says the mesh has:

• 4 vertices

• 2 triangles

• 6 edges

• 6 borderedges

so all edges are considered unique for some reason in this case. (for some other meshes it works, but clearly not on all)