pre vs. post increment and operator overloading

I wrote a trivial class to test operator overloading - see below. 
In Main() I post increment and assign an int.
The assignment happens before the increment - no suprise.
I then perform the equivalent operation on the Test class instance and the assert fails.
Can someone tell me why  Cheers.







using System;
using System.Diagnostics;
namespace test_overloading {
   class Test {
      private int m_value = 0;
 
      static void Main(string[] args) {

         int i = 0;
         int j = i++; //assign then increment
         Debug.Assert(!i.Equals(j));
         Test t1 = new Test();
         Test t2 = t1++; //assign then increment
         Debug.Assert(!t2.Equals(t1));
      }

      public static Test operator++(Test t) {
         t.m_value++;
         return t;
      }

      public bool Equals(object rhs) {
         if ( !(rhs is Test) ) return false; //if type differs not equal
         Test t = (Test)rhs; //cast must succeed
         //objects are equal if m_value members are equal
         return (m_value == t.m_value);
      }
   }
}