HTTP POST receiving more than one HTTP Response - asp.net

Question

I have an http POST being actioned via a .NET System.Net.WebRequest as follows:
...
XXXUtilities.Log.WriteLog(string.Format("XXXHTTPPost PostToUri has uri={0}, body={1}", uri, messageBodyAsString));
System.Net.WebRequest req = System.Net.WebRequest.Create(uri);
req.ContentType = "application/x-www-form-urlencoded";
req.Method = "POST";
byte[] bytes = System.Text.Encoding.ASCII.GetBytes(messageBodyAsString);
req.ContentLength = bytes.Length;
System.IO.Stream os = req.GetRequestStream();
os.Write(bytes, 0, bytes.Length);
os.Close();
try
{
using (System.Net.WebResponse resp = req.GetResponse())
{
if (resp == null) return null;
System.IO.StreamReader sr =
new System.IO.StreamReader(resp.GetResponseStream());
string rs = sr.ReadToEnd().Trim();
sr.Close();
resp.Close();
XXXUtilities.Log.WriteLog(string.Format("XXXHTTPPost PostToUri has string response = {0}", rs));
MongoDB.Bson.BsonDocument doc2 = new BsonDocument();
doc2.Add("Response", rs);
return doc2;
}
}
catch (System.Net.WebException e)
{...
This all works fine most of the time. However, looking at the log files that this creates I spotted something strange. The suspect log entries look like this:
18:59:17.0608 HPSHTTPPost PostToUri has uri=https://salesforce.ringlead.com/cgi-bin/2848/3/dedup.pl, body=LastName=Doe&FirstName=Jon
18:59:17.5608 HPSHTTPPost PostToUri has string response = Success
18:59:18.0295 HPSHTTPPost PostToUri has string response = Success
It seems that the Http Response is being received twice. Is this even technically possible? i.e. is it possible for an Http POST to receive two Responses, one after the other? If so, is my code below then liable to be called twice, thus resulting in the observed log file entries? Many thanks.
Edit:
In response to the comment that the logging code may be broken, here is the logging code:
public class Log
{
public static void WriteLog(string commandText)
{
string clientDBName = "test";
string username = "test";
try
{
string filePath = "c:\\Data\\XXXLogs\\" + clientDBName + "logs\\";
string filename = System.DateTime.Now.ToString("yyyyMMdd_") + username + ".log";
DirectoryInfo dir = new DirectoryInfo(filePath);
if (!dir.Exists)
{
dir.Create();
}
System.IO.FileStream stream = new System.IO.FileStream(
filePath + filename
, System.IO.FileMode.Append); // Will create if not already exists
StreamWriter writer = new StreamWriter(stream);
writer.WriteLine(); // Writes a line terminator, thus separating entries by 1 blank line
writer.WriteLine(System.DateTime.Now.ToString("HH:mm:ss.ffff") + " " + commandText);
writer.Flush();
stream.Close();
}
catch { }
}
}