Thanks TristanKazu for the repro...I took a look at this...looks like the problem is because of the type of return type that you are using when defining the OData action...
Change the following code:
Change the following code:
usersAction.Returns<HttpResponseMessage>();
to say something like below:usersAction.Returns<string>();
The thing is you would want to mention the 'actual' type that you are sending back to the client, which in this case is of type 'string'. I haven't verified this with older bits but this would be the expected way to do.