The benefit is that the window doesnt scroll as you are trying to select a menu item based on the nickname you right clicked on. If the window scrolled off after you right clicked a nick, you would no longer be able to confirm what it is you had right clicked on. I personally wouldn't trust clicking "Op" on a nick if I couldn't see the nick I had clicked on behind my mouse. Popups don't show the nick, so context relies on where the popup is in relation to your buffer at the time of click.
If it's designed this way, there is unlikely to be any workaround.
