This happens in .NET Framework 3.5, 32 bit, VS 2008.

C#:

namespace NesterovskyBros.Test
{

  using Microsoft.VisualStudio.TestTools.UnitTesting;

  [TestClass]
  public class CharAtUnitTest
  {
    private TestContext testContextInstance;

    public TestContext TestContext
    {
      get { return testContextInstance; }
      set { testContextInstance = value; }
    }

    [TestMethod]
    public void CharAtTest()
    {
      this.text = "1";

      string token = Read(1, false);

      TestContext.WriteLine("token: {0}", token);
    }

    private string Read(int offset, bool flag)
    {
      string token = null;
      int c = 0;

      if (flag)
      {
        goto Whitespace;
      }

    Scan:
      c = CharAt(offset);

      switch(c)
      {
        case -1:
        {
          return "<Eof>";
        }
        case '\'':
        {
          token = "Literal";

          goto Literal;
        }
      }

    Whitespace:
      if (c == ' ')
      {
        return "Space";
      }

      return "Unknown";

    Literal:
      while(true)
      {
        int d = CharAt(offset);

        if (token != "Literal")
        {
          goto Scan;
        }

        if (d == c)
        {
          return token;
        }
      }
    }

    string text;

    private int CharAt(int offset)
    {
      string text = this.text;

      return (uint)offset >= (uint)text.Length ? -1 : text[offset];
    }
  }
}

In debug mode this test prints: "token: <Eof>". In release - "token: Unknown". The bug is so fragile that even slightest change in code removes it. Looking into disassembly we can see that the problem is near the switch:

    Scan:
      c = CharAt(offset); /* Our old friend, CharAt(). Inlined! */
00000017 mov edx,dword ptr [edi+8]
0000001a cmp dword ptr [edx+8],esi
0000001d jbe 00000032
0000001f cmp esi,dword ptr [edx+8]
00000022 jae 000000CE
00000028 movzx eax,word ptr [edx+esi*2+0Ch]
0000002d mov dword ptr [ebp-10h],eax
00000030 jmp 00000039
00000032 mov dword ptr [ebp-10h],0FFFFFFFFh /* Move -1 (four bytes) into stack. */
00000039 movzx edx,word ptr [ebp-10h] /* Get two bytes into edx (0FFFFh) */

      switch(c)
0000003d cmp edx,0FFFFFFFFh /* Never true. */
00000040 je 0000004A
00000042 cmp dword ptr [ebp-10h],27h
00000046 je 0000005A
00000048 jmp 00000062
      {
        case -1:
        {
          return "<Eof>";
0000004a mov eax,dword ptr ds:[022EDE68h]
00000050 lea esp,[ebp-0Ch]
00000053 pop ebx
00000054 pop esi
00000055 pop edi
00000056 pop ebp
00000057 ret 4

This looks like a tremendous bug, like one of those shaking belief in computer's infallibility.

It would be nice if you would verify the case on your computer.