ADO.NET Data Service Doesn't Update

I've a problem updating objects with the ADO.NET Data Services.

First I've create a service, which can load and store the data. Its a basic data context which implements the IUpdatable-interface.

After that, I've created a simple service-client. I just created it with the 'Add Service'-reference in Visual Studio. Basically this service seams to work. I can query for the objects and store new objects. However I cannot update objects.

This is my update-code on the client:

var ctx =
new TeamDataContext(new Uri("http://localhost:8637/TeamInfoService.svc"));
var team = ctx.Teams.First();
team.TeamName = "New Team Name";
ctx.UpdateObject(team);
ctx.SaveChanges();

What my main issue is, that IUpdatable.SetValue() isn't called for the object which I want to update. Only the IUpdatable.SaveChanges() is called without updating the objects on the server.

When I create a new object, the IUpdatable.SetValue is called on the server to set the property.

So what I am doing wrong? Are my expectations wrong? Is IUpdatable.SetValue supposed to be called when updating a object? Or do I need to do additional things to do updates?

Edit: I just watched the HTTP-requests between the client and the server. The client send a HTTP-Merge request with the changes. However I still don't know why the changes aren't stored.