In this case it's a bug, as I'm not trying to 'disable' the mouse, but track scrolling and then make the menu 'stick' to the header when the user scrolls down t

In this case it's a bug, as I'm not trying to 'disable' the mouse, but track scrolling and then make the menu 'stick' to the header when the user scrolls down the page. A common design pattern which increases usability quite a bit.