UDP with UWP behaves different - udp

Question

I wrote an app which sends an UDP datagram. If I try it on a Computer with Windows 10 on, it works, the other device (a Commercial one) responds correctly. If I execute the same app on an Windows 10 IoT (Raspberry Pi2), the device does not respond. First tought was a Firewall Problem. Thus I had a look on traffic with WireShark. In both cases the datagrams send over the WLAN, are the same. In case of Windows 10 I see the response from the device, in case of IoT there is no response.
Here is the method I use to send the datagram:
private async void FindDevice()
{
DatagramSocket socket = new DatagramSocket();
socket.MessageReceived += Socket_MessageReceived;
IPAddress ipAddressOfSender;
// device must be in the same network
if (IPAddress.TryParse("192.168.0.1", out ipAddressOfSender))
{
byte[] broadcastIpAddress = ipAddressOfSender.GetAddressBytes();
// Assuming to work with a class C IP address, so broadcast address looks like a.b.c.255
broadcastIpAddress[3] = 255;
using (var stream = await socket.GetOutputStreamAsync(new HostName(new IPAddress(broadcastIpAddress).ToString()), SendingPort.ToString()))
{
using (var writer = new DataWriter(stream))
{
byte[] helloSmartPlugs = { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0x45, 0x44, 0x49, 0x4d, 0x41,
0x58, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xa1, 0xff, 0x5e };
writer.WriteBytes(helloSmartPlugs);
await writer.StoreAsync();
}
}
}
}
In some samples there is also bound the listener port. It doesn't matter, if I do that or not, it still works on Windows, but not IoT. Can that someone explain me? I assumed I Need the listener port.
What could be the reason, the device does not answer in case of IoT? Are there Settings I have to provide with the socket?