RO's nades are thrown in an arc, ie they have quite a high angle relative to your POV. It'll go up and out of your view and for some f*** reason your nade will bounce off the wall when you were looking RIGHT AT the window. =P
It's a real subtle thing but people seem to have difficulty with it; you have to get used to it. You often have to be looking towards/at the ground depending on how close you are to the window, door etc. If you can get a handle on it you can be quite accurate, and you only TK when one of your bros rushes in or you didn't know they were there anyway.
Play around in SP or on a bot server to get a feel for the angle and it will end up being second nature. Personally I hate nades, I drop the things on spawn. I'm very good at shooting my teammates though. #colorblind five