Seemingly they missed the lesson web developers learned ten years ago that you can't change content that the user is currently looking at without any interaction done, unless that's to be expected from the user.
But auto-loading items in a list is somehow still difficult for these companies to get right. Once you're done typing your query in the window's start menu, apple's "quick launcher thing" or twitter's search widget, it takes X seconds for the query to actually finish, so while you're hovering the menu, it changes content from underneath and the thing you wanted to click on, has been switched to something else.
I'm starting to wonder if this is on purpose, as seemingly no one is getting this right, but I don't understand what metric they are optimizing for (incorrectly) to believing that this behavior is correct.