On Demand Patching is a feature that can be turned off or on within the Launcher. In order to turn it off or on, please take a moment to launch the game and once the launcher is up and running, in the upper right-hand corner is the text link titled "Options." Go ahead and click on that and a smaller dialog box will appear. Toward the bottom of this new box is the option "Disable On Demand Patching." Ensure there's a check in that box to disable it and then go forward with launching the game.
At the very least, this procedure will walk you though disabling this pesky feature.