This bug where you cant highlight/select "Trade with player" when you right-clicked on a runner has a very simple workarround. I always assumed everyone already knowed this one coz it's so damn easy, but I noticed that that's not the case. So here it goes:
DONT HAVE ANY RPOS WINDOWS OPEN BEHIND THE "TRADE WITH PLAYER" WINDOW
Yup. Thats it. This inlcudes all the F1-F11 windows, "details"-windows, etc...