Hello everyone.
I'm trying to use Windows sockets to send and receive UDP packets (in C++).
It worked well until three days ago, when the program stopped behaving properly.
To summarize the situation:

• When calling WSAPoll() on my socket, it always returns my socket updated with EVERY revents possible (corresponding to every events I gave the pollfd), even if there is no server launched.
• When calling recvfrom() and no server is launched, it returns SOCKET_ERROR with error code 10054(*).
• When calling recvfrom() and a server is launched, it works properly – blocks until it receives something.
• The behavior is the same whether I try to connect to localhost or to a distant host.

(*) I investigated this error. In UDP, it means that there is an ICMP problem. ("On a UDP-datagram socket this error indicates a previous send operation resulted in an ICMP Port Unreachable message.").
I indeed call sendto() before recvfrom(), so the problem's not here.
I tried to put down my firewall to see if it changed anything, but it didn't. I also tried to put down every network flowing through my PC. In this state I managed to get the program to work for a few minutes, but when I enabled the networks it stopped working again. I tried to repeat the process but it would not work anymore.
I tried compiling with both visual studio (2015) and MinGW.
I tried on another computer too (under Windows 7, mine has Windows 8.1), to no avail.

Here is a simple test file which does not work on my computer.

#undef _WIN32_WINNT
#define _WIN32_WINNT 0x501
#include <winsock2.h>
#include <ws2tcpip.h>
#include <stdio.h>
#include <vector>
#include <iostream>

int main() {
  int clientSock;
  char buf[100];
  int serverPort;

  /* Initializing WSA */
  WSADATA wsaData;
  WSAStartup(MAKEWORD(2, 2), &wsaData);

  /* I create my socket */
  struct addrinfo specs;
  struct addrinfo *addr = new addrinfo;
  ZeroMemory(&specs, sizeof(specs));
  specs.ai_family = AF_INET;
  specs.ai_socktype = SOCK_DGRAM;
  specs.ai_flags = 0;
  getaddrinfo("127.0.0.1", "2324", &specs, &addr);

  clientSock = socket(addr->ai_family, addr->ai_socktype, addr->ai_protocol);

  /* I get the server's address */
  struct sockaddr_in serverAddr;
  serverAddr.sin_family = AF_INET;
  serverAddr.sin_addr.s_addr = inet_addr("127.0.0.1");
  serverAddr.sin_port = htons(2324);
  int len = sizeof(struct sockaddr);

  /* I'll poll & recvfrom on my socket */
  std::vector<pollfd> fds;
  pollfd fd;
  fd.fd = clientSock;
  fd.events = POLLRDNORM;
  fd.revents = -1;
  fds.push_back(fd);

  while(1) {
    memset(buf,0,sizeof(buf));
    printf("\nClient--->: ");
    gets(buf);
    /* It's UDP, so it doesn't matter if there is someone to receive the packet */
    sendto(clientSock, buf, strlen(buf), 0, (sockaddr*)&serverAddr ,len);

    memset(buf,0,sizeof(buf));
    int ret;
    /* Always returns "1" */
    if ((ret = WSAPoll(fds.data(), 1, 0)) > 0) {
      std::cout << ret;
      /* Always returns "-1" */
      std::cout << recvfrom(clientSock,buf,sizeof(buf),0, (sockaddr*)&serverAddr,&len) << std::endl;
      printf("\n--->From the server: ");
      printf("%s",buf);
    }
  }

  closesocket(clientSock);
  WSACleanup();

  return 0;
}

Two questions:

1. Why does WSAPoll() always returns an updated socket, even if there wasn't any interaction with it ?
2. Why does recvfrom() return this error and how can I fix it ? I suppose it comes from my computer. I tried allowing ICMP through my firewall but it didn't change anything, maybe I did something wrong ?

Edit: I fixed my main program (not shown here because it is way too large) by just ignoring any "error 10054" I received. Now it works the same way it does on Unix.
Still, it is not really a solution (ignoring an error code… meh) and if anyone knows why I get the "ICMP Port Unreachable" error when calling sendto(), I'd be glad to hear about it.