Java Robot won't navigate dropdown menu with keypress

I’m using Java robot to script a boring task and everything is working fine except when I try to navigate a dropdown menu using

robot.keyPress(VK_DOWN);
robot.keyRelease(VK_DOWN);

VK_UP, VK_END and so on isn’t working either.
Simply nothing happens. Everything else works, moving mouse, clicking, typing in a textfield… I’m doing it in Safari.