Na all other hotkeys get saved so.... only this particular one doesnt.Grave is °(§)? So you have the same keyboard style as i have. Hmm but i don't know the solution. Does it change after you restart the game? Or does it change between two games without leaving the online lobby.
For example if you change the config. in CSS ingame, it won't be saved. It'll just be changed for that session -> until you restart the game. To save the changes you need to change it in windows and save it.
Perhaps it's the same for C&C3.