So, yes, this is exactly the window size detection feature in action that makes sure any sub menu is displayed within the browser viewport and all items are accessible. The feature is controlled with the keepInViewport: true/false option.
No need to pay anything for this, it’s an essential built-in feature. BTW, it gets more interesting when your sub menus are long enough to not fit entirely in the viewport height. You can test that too if you like, just play with the fiddle.. 🙂
PS: I am Vasil Dinkov – using admin, just makes it clearer to other forum users that I am actually the forum admin and am directly associated with the project.