I have just posted this on the ATC forum, but its about the same subject so I will copy it here as well.
As far as I am aware, the RPAR fix will be rolled out this summer and therefore hopefully the problem will go away. However, the reason that you have to select the ac contact that you are going to provide a talkdown to is fairly simple. When you select the ac the system allocates extra beams from the surveillance side of its workings to track the ac that you are interested in (13 I believe) this enables the system to obtain the level of accuracy required in order to provide a talkdown.
As for going back to CR62, I think the problems with RPAR have made you nostalgic for a past that never existed. If you want: excessive clutter, contacts the size of mars bars, survoing, utter confusion when doing 2 talkdowns at once, a system that you had to physically lock down in high winds, mechanically turning gears that took 10 mins to change runway (if they didn’t stop halfway through), a system that spent half it’s life on maintenance, a DH cursor that you had to be a safe cracker to set right and endless knobs switches and buttons to press in an attempt to make the picture work then you are welcome to it. As far as I can see RPAR is a welcome step forward, yes, it has had its problems but half of them were our own bloody fault. Who trials a new system in the Falkland Islands and then never goes down to see it, or appreciate what it will do in a busy environment. What company gives you a multi-million pound piece of kit but then doesn’t tell you how to operate it until it has been installed for over a month.
The introduction of RPAR has seen its fair share of problems, but has exposed us in ATC to the big bad world of procurement, and we have looked a little naive to its ways to say the least.
Go back to your CR62 Luddite, but I guarantee that within 2 years you will be sitting in front of a blank screen, because no company on Earth will be manufacturing the wiggly bits inside it.