I was about to upgrade my DIR-825 to 1.51 since I had the same wifi issue. And a weird thing happened. All the settings were gone after I tried to reboot the machine every single time.

Actually it had happened when I tried to use the image file that I compiled myself. I thought it might be some minor issue of testing build. Therefore, I went back to 1.5.0, and everything was fine except wifi.
Now the latest build has the same problem. I have tried v1.4.4 version, which works fine on DIR-825 (at least it keeps the settings)
So does anyone know what the problem might be?