C# Unity3D Error: List<int>.ToArray() problem

I'm building a complex mesh via C# scripting in Unity3D. Following my generation codes, I pass my triangle data to UnityEngine.Mesh.triangles. My triangle data is stored in a variable typed as List<int>. And the type of UnityEngine.Mesh.triangles is int[]. So I used List<int>.ToArray() method to convert it. But after conversion, some items in the UnityEngine.Mesh.triangles(int[]) are not identical to my triangle data(List<int>). To be more specific, I found that List<int> typed variables could store numbers greater than 65535, but int[] can not do that.

codes:

List<int> ts = new List<int>();
//generation codes
mesh.triangles = ts.ToArray();

And I use this code to test it in Unity:

for (int i = 0; i < mesh.triangles.Length; i++)
            if (mesh.triangles[i] != ts[i]) Debug.Log(mesh.triangles[i].ToString() + " ≠ " + ts[i].ToString()); 

then I get logs such as 0≠65536, indicating that there is a overflow.