Late-appearing elements are really annoying as well. They like appear under your mouse the moment you want to click on something.
But nowadays - a background thread will search for the stuff that should appear in the UI, and adds that directly when it found something.
You can solve the problem by changing the mouse icon to the hourglass, blocking the UI for just enough time to not get any accidental clicks, and update it.
As side effect, every update now takes some time - so you have to minimize the number of updates.
(Discloseure: I work at Google, speaking only for myself)