Something weird's happening here..

I've made a 24 puzzle, and it's working okay apart from its initialization.

Code (csharp):

1.  
2.     [HideInInspector] public int empty;
3.     [HideInInspector] public TileScript[] TS = new TileScript[26];
4.     [HideInInspector] public int wrong;
5.     [HideInInspector] public int pending;
6.     public Text movesTakenText;
7.     public Text solvableText;
8.     int moves = 0;
9.     int movedTile;
10.     private bool _b = true;
11.     public bool canMove {/*get/set*/}
12.  
13.     public void ShuffleTiles (){
14.         int[] order = new int[26];
15.         Sprite[] sprt = new Sprite[26];
16.         bool isSolvable = false;
17.         for (int i = 0; i <= 25; i++) {
18.             order [i] = TS[i].tile;
19.             sprt [order[i]] = TS [i].spr;
20.         }
21.         pending = 0;
22.         wrong = 0;
23.         int inversions = 0;
24.         int a;
25.         int b;
26.         while (!isSolvable || order[0] == 0) {
27.             Shuffle (order);
28.             for (int i = 1; i < order.Length; i++) {
29.                 a = order [i];
30.                 if (a != 0) {
31.                     for (int j = 1; j < i; j++) {
32.                         b = order [j];
33.                         if (b != 0) {
34.                             if (b > a) inversions++;
35.                         }
36.                     }
37.                 } else {
38.                     empty = i;
39.                 }
40.             }
41.             isSolvable = inversions % 2 == 0 && (Row (empty) - Row (order [0])) % 2 == 0;
42.         }
43.         for (int i = 0; i <= 25; i++) {
44.             TS [i].tile = order [i];
45.             TS [i].spr = sprt [order [i]];
46.             if (!TS [i].correct && i > 0 && order[i] != 0) wrong++;
47.         }
48.         moves = 0;
49.         movesTakenText.text = "Moves: 0";
50.         solvableText.text = "Unchecked";
51.         canMove = true;
52.     }
53.  
54.     public void CheckIfSolvable(){
55.         int[] order = new int[26];
56.         int a;
57.         int b;
58.         int inversions = 0;
59.         for (int i = 0; i <= 25; i++) {
60.             order [i] = TS[i].tile;
61.         }
62.         for (int i = 2; i < order.Length; i++) {
63.             a = order [i];
64.             if (a != 0) {
65.                 for (int j = 1; j < i; j++) {
66.                     b = order [j];
67.                     if (b != 0) {
68.                         if (b > a) inversions++;
69.                     }
70.                 }
71.             }
72.         }
73.         if ((inversions % 2 == 0 && (Row (empty) - Row (order [0])) % 2 == 0)) {
74.             solvableText.text = "Solvable";
75.         } else {
76.             solvableText.text = "Unsolvable";
77.         }
78.     }
79.  
80.     public static void Shuffle<T>(T[] array)
81.     {
82.         System.Random rand = new System.Random();
83.         int m = array.Length;
84.         for (int i = 0; i < m; i++)
85.         {
86.             int idx = rand.Next(i, m);
87.             T tmp = array[i];
88.             array[i] = array[idx];
89.             array[idx] = tmp;
90.         }
91.     }
92.  
93.     public static int Row(int i){
94.         return (i-1) / 5;
95.     }
96.  
97.     public static int Col(int i){
98.         return (i-1) % 5;
99.     }
100.  

The [0] tile is the missing one, and I initiate the TS (TileScript)s in another script.
And I can call the "ShuffleTiles" and "CheckIfSolvable" via UI buttons;

So the problem is:
I have the "CheckIfSolvable" method integrated into the "ShuffleTiles" method, and I'm shuffling the order until the puzzle is solvable (with the while), however the puzzles don't always start solvable. When I use the "CheckIfSolvable" after a shuffle - they aren't always solvable.
Any idea why is that happening?