Only do the custom decompression on mono.

src/NzbDrone.Common/Http/Dispatchers/ManagedHttpDispatcher.cs

@@ -26,18 +26,26 @@ namespace NzbDrone.Common.Http.Dispatchers
         {
             var webRequest = (HttpWebRequest)WebRequest.Create((Uri)request.Url);
 
-            // Deflate is not a standard and could break depending on implementation.
-            // we should just stick with the more compatible Gzip
-            //http://stackoverflow.com/questions/8490718/how-to-decompress-stream-deflated-with-java-util-zip-deflater-in-net
-            webRequest.AutomaticDecompression = DecompressionMethods.None;
-
+            if (PlatformInfo.IsMono)
+            {
+                // On Mono GZipStream/DeflateStream leaks memory if an exception is thrown, use an intermediate buffer in that case.
+                webRequest.AutomaticDecompression = DecompressionMethods.None;
+                webRequest.Headers.Add("Accept-Encoding", "gzip");
+            }
+            else
+            {
+                // Deflate is not a standard and could break depending on implementation.
+                // we should just stick with the more compatible Gzip
+                //http://stackoverflow.com/questions/8490718/how-to-decompress-stream-deflated-with-java-util-zip-deflater-in-net
+                webRequest.AutomaticDecompression = DecompressionMethods.GZip;
+            }
+            
             webRequest.Method = request.Method.ToString();
             webRequest.UserAgent = _userAgentBuilder.GetUserAgent(request.UseSimplifiedUserAgent);
             webRequest.KeepAlive = request.ConnectionKeepAlive;
             webRequest.AllowAutoRedirect = false;
             webRequest.CookieContainer = cookies;
 
-            webRequest.Headers.Add("Accept-Encoding", "gzip");
 
             if (request.RequestTimeout != TimeSpan.Zero)
             {
@@ -111,8 +119,7 @@ namespace NzbDrone.Common.Http.Dispatchers
                     {
                         data = responseStream.ToBytes();
 
-                        // Do our own decompression.
-                        if (httpWebResponse.ContentEncoding == "gzip")
+                        if (PlatformInfo.IsMono && httpWebResponse.ContentEncoding == "gzip")
                         {
                             using (var compressedStream = new MemoryStream(data))
                             using (var gzip = new GZipStream(compressedStream, CompressionMode.Decompress))