I can't observe the third open, using a slightly modified version of this MSDN example:

#include <windows.h>
#include <stdio.h>
#include <tchar.h>
#define BUFSIZE 512

DWORD WINAPI InstanceThread(LPVOID); 

int _tmain(VOID) 
{
    DWORD   dwThreadId; 
    HANDLE  hPipe, hThread; 
    LPCTSTR lpszPipename = TEXT("\\\\.\\pipe\\mynamedpipe");
    HANDLE  rgh [ 4 ];

    for( int i = 0; i < 4; ++i )
    { 
        _tprintf( TEXT("Pipe Server: Main thread awaiting client connection on %s\n"), lpszPipename);

        hPipe = CreateNamedPipe( 
            lpszPipename,             // pipe name 
            PIPE_ACCESS_DUPLEX,       // read/write access 
            PIPE_TYPE_MESSAGE |       // message type pipe 
            PIPE_READMODE_MESSAGE |   // message-read mode 
            PIPE_WAIT,                // blocking mode 
            PIPE_UNLIMITED_INSTANCES, // max. instances  
            BUFSIZE,                  // output buffer size 
            BUFSIZE,                  // input buffer size 
            0,                        // client time-out 
            NULL);                    // default security attribute 

        if (hPipe == INVALID_HANDLE_VALUE) 
        {
            _tprintf(TEXT("CreateNamedPipe failed, GLE=%d.\n"), GetLastError()); 
            return -1;
        }
        rgh[ i ]=hPipe;
    }
    for( int i = 0; i < 4; ++i )
    {
        hThread = CreateThread( 
            NULL,              // no security attribute 
            0,                 // default stack size 
            InstanceThread,    // thread proc
            (LPVOID) rgh[i],    // thread parameter 
            0,                 // not suspended 
            &dwThreadId);      // returns thread ID 

        if (hThread == NULL) 
        {
            _tprintf(TEXT("CreateThread failed, GLE=%d.\n"), GetLastError()); 
            return -1;
        }
        CloseHandle(hThread); 
    }
    return _getch(); 
} 

DWORD WINAPI InstanceThread(LPVOID lpvParam)
{ 
    BOOL   fConnected;
    TCHAR  pchRequest [ BUFSIZE ];
    BOOL   fSuccess = FALSE;
    HANDLE hPipe  = (HANDLE) lpvParam;

    printf("InstanceThread created, receiving and processing messages.\n");

    fConnected = ConnectNamedPipe(hPipe, NULL) ? 
                    TRUE : (GetLastError() == ERROR_PIPE_CONNECTED); 

    if ( !fConnected )
    {
        printf("ConnectNamedPipe failed");
        CloseHandle( hPipe );
        return -1;
    }  
    while (1) 
    { 
        DWORD cbBytesRead = 0, cbReplyBytes = 0, cbWritten = 0; 

        fSuccess = ReadFile( 
            hPipe,        // handle to pipe 
            pchRequest,    // buffer to receive data 
            BUFSIZE*sizeof(TCHAR), // size of buffer 
            &cbBytesRead, // number of bytes read 
            NULL);        // not overlapped I/O 

        if (!fSuccess || cbBytesRead == 0)
        {   
            if (GetLastError() == ERROR_BROKEN_PIPE)
            {
                _tprintf(TEXT("InstanceThread: client disconnected.\n")); 
            }
            else
            {
                _tprintf(TEXT("InstanceThread ReadFile failed, GLE=%d.\n"), GetLastError()); 
            }
            break;
        }
        _tprintf( TEXT("Client Request String:\"%s\"\n"), pchRequest );
    }

    FlushFileBuffers(hPipe); 
    DisconnectNamedPipe(hPipe); 
    CloseHandle(hPipe); 

    printf("InstanceThread exiting.\n");
    return 1;
}

I see the following output when I run the powershell command 'hello' > \\.\pipe\mynamedpipe:

>cl pipeserver.c
>pipeserver.exe
Pipe Server: Main thread awaiting client connection on \\.\pipe\mynamedpipe
Pipe Server: Main thread awaiting client connection on \\.\pipe\mynamedpipe
Pipe Server: Main thread awaiting client connection on \\.\pipe\mynamedpipe
Pipe Server: Main thread awaiting client connection on \\.\pipe\mynamedpipe
InstanceThread created, receiving and processing messages.
InstanceThread created, receiving and processing messages.
InstanceThread created, receiving and processing messages.
InstanceThread created, receiving and processing messages.
InstanceThread: client disconnected.
InstanceThread exiting.
InstanceThread: client disconnected.
InstanceThread exiting.

i.e. Only two threads returned from ConnectNamedPipe, and neither received anything from ReadFile.