WCF method called twice

Question

I have a web service which is returning data to the desktop application. The problem I am having is, when the web service returns small volume of data everything works fine but

Answer 1

I ran into the exact same symptoms as OP, but my target was an Oracle webservice that I have no control over. WebService calls worked fine from a standalone test web-application, but not from the .NET app that required the implementation.

I don't understand why, but updating the targetFramework in web.config from 4.5 to 4.6.1 fixed the issue for my application.

<httpRuntime targetFramework="4.5" requestValidationMode="4.5" executionTimeout="36000" />

<httpRuntime targetFramework="4.6.1" requestValidationMode="4.5" executionTimeout="36000" />