False memory leaks on Visual Studio with OpenCV and MFC is a known "false" problem. Even if the solution is easy a lot of people is looking for. This article shows the solution step by step.
If you create a DLL that using runtime library then DLL's client application must load required runtime library. If runtime libs loaded by client application aren't same than required by your DLL you will have "unable to run your application. MSVCR80 was not found...."