I am experienceing the same problem. In fact, you can remap using EasySearch, but you must run through the configuration first. You need not change any of your configuration settings, you understand; you merely need to run through it.
Instead, of course, you can remap using Windows "run" menu. From Start|Run, input the IP address of your DNS-323 (eg: "\\192.168.1.101", not including the quotes), select your volume (eg: "volume_1"), right-click on it, select "map network drive" and remap your drive to the letter you want.
Of course, neither of these suggestions clears up the fact that you are losing this mapping, but at least you can re-establish it fairly easily. Good luck...