Dropdown menu opens even if clicked outside

Is there some trick to the uGUI Dropdown menu that I am missing? After interacting with one and then clicking anywhere, the Dropdown menu opens again, which makes it difficult/impossible to interact with other GUI elements.

I already set the Navigation option to none, both in the Dropdown and the Item-Template, but this didn’t have an effect.

I tracked it down. It was a problem with my Input Settings. I had an alias for Submit/Cancel using the mouse buttons.