Hi,
If you have it connected it to the RTS line as shown it should work as stated previously, the recieve line should go hiZ if the RTS line is high so there should be no local echo. Do you have a short on your board or is the receiving device on the RS485 echoing back the characters if they are not recognised. Do you get this if nothing is plugged into the RS485? Have you got the A/B lines the correct way round they join to their own letter at all nodes, with RS485 do not cross them like RS232. This might cause a local echo but I am guessing as I have not seen it happen in practice (yet).
Bob