asyncSupported = false and still "Installed AtmosphereHandler" ?

Now I don’t leverage Push (Websockets) in my application. I have set asyncSupported = false.
@WebServlet(urlPatterns = ["/*"] , name = "MyServlet", asyncSupported = false), but I still see in the log messages like Installed AtmosphereHandler …
Why Vaadin starts Websockets handlers based on Atmosphere when asyncSupported = false ?