IndexOf C#出错

我正在编写一个函数,它返回由特定字符串分隔的子字符串数.
这是一个相当简单的功能 –

public static FuncError DCount(String v1,String v2,ref Int32 result) {
        result = 0;
        if (String.IsNullOrEmpty(v1)) {
            return null;
        }
        if (String.IsNullOrEmpty(v2)) {
            return null;
        }

        int ct = 1;
        int ix = 0;
        int nix = 0;

        do {
            nix = v1.IndexOf(v2,ix);
            if (nix >= 0) {
                ct++;

                System.Diagnostics.Debug.Print(
string.Format("{0} found at {1} count={2} result = {3}",v2,nix,ct,v1.Substring(nix,1)));
                ix = nix + v2.Length;
            }
        } while (nix >= 0);
        result = ct;
        return null;
    }

当我使用在特定情况下用作分隔符的特殊字符调用时会出现问题.它返回了许多误报.从Debug.Print开始,第一个和最后一个参数应始终相同.

t found at 105 count=2 result = t
t found at 136 count=3 result = t
t found at 152 count=4 result = t
t found at 249 count=5 result = t
t found at 265 count=6 result = t
t found at 287 count=7 result = t
t found at 317 count=8 result = t
t found at 333 count=9 result = t
t found at 443 count=10 result = t
t found at 553 count=11 result = t
t found at 663 count=12 result = t
t found at 773 count=13 result = t
t found at 883 count=14 result = t
t found at 993 count=15 result = t

如果我将pass作为char传递它可以正常工作.
如果我使用split作为分隔符拆分字符串,则返回正确数量的元素.
至于错误识别的’t’,结果中还有其他’t’未被拾取,因此它不是字符转换问题.

困惑……

谢谢