I've tried to duplicate but this works fine for me. I'm using Tableau Desktop 8.1.6. Sorry I couldn't help out.
I am not seeing it either. Any chance you're using any kind of non-typical setup, like a Mac with VM or something?
I see this happen too, if you move the mouse down after pressing the search magnifying glass and before typing.
This problem does not reproduce for me in 8.2.
8.2 fixed the issue!