When I looked at my blog I found that “No Categories” was mentioned under the Categories head. So first I refreshed the browse but with no avail then I checkd the Presentation to find out if anything is wrong. I tried to change the theme also but the problem still presisted. Then I tried to look other blogs all had the same problem.
So, hopefully if it is not technical glitch, then I believe there WP may making some changing in Category feature.