The Add/Remove buttons jumps around when the window is resizing(which is good). When I'm about to add the next plugin I waste energy on chasing the buttons. I run into this issue often, and there is a simple solution to it. My suggestion is one of two places, as per the attached images.
I have a hard time believing I'm alone getting annoyed by this?
My own preference is if the buttons resided in the list area, where it doesn't mess visually with the top menu.