Stored procedure enumeration not yielding any results

Stored procedure enumeration not yielding any results

I'm trying to execute a stored procedure in my project, but the
enumeration is not yielding any results.
Why? What am I doing wrong?
Info about my project:
.NET Framework 4.5
<package id="EntityFramework" version="5.0.0" targetFramework="net45" />
Microsoft SQL Server 2008 (SP3) - 10.0.5500.0 (X64)
Manually using stored procedure works and returns the correct data:
DECLARE @return_value int
EXEC @return_value = [dbo].[GetFeatures]
@XMLDoc =
N'<ArrayOfInt><int>280</int><int>286</int><int>279</int><int>292</int><int>277</int></ArrayOfInt>',
@ReleaseId = 340
SELECT 'Return Value' = @return_value
Here's where I execute the stored procedure in my code:
public ObjectResult<GetFeatures_Result> GetFeatures(List<int> featureIds,
int releaseId, int? timeboxId, int? teamId)
{
string xmlFeatureIds = null;
var xs = new XmlSerializer(typeof(List<int>));
var ms = new MemoryStream();
xs.Serialize(ms, featureIds.ToList());
//xmlFeatureIds = Encoding.UTF8.GetString(ms.ToArray());
xmlFeatureIds =
"<ArrayOfInt><int>280</int><int>286</int><int>279</int><int>292</int><int>277</int></ArrayOfInt>";
//releaseId = 340;
var release = _rmContext.Releases.FirstOrDefault(x => x.Id ==
releaseId);//works, Releases is just a table
var obj = _rmContext.GetFeatures(xmlFeatureIds, releaseId, null,
null); //enumeration didn't yield any results
var obj2 = _rmContext.GetFeatures(xmlFeatureIds, releaseId, null,
null).ToList(); //length of this is zero.
return obj;
}
Model browser and visual studio setup: