Thanks a lot for the info! Will do these when I have time. Some of my packages were manually installed... ouch!
I solved the problem by a clean install. Just modify /etc.defaults/VERSION for downgrade, and after picking the install/upgrade option at menu. Select connect or double click NAS in assistant, web GUI will be brought up. Select install there, and the second option will be a clean install with all files kept. The sad point is even with configuration backup, all packages installed will need to be resintalled. Users can be restored, some permissions might need to be double checked. Optware need to be reinstalled. But at least I get the issue resolved.