Filtering tags by name only lets you view them by popularity.
Today I was searching for some tags under Super User's "Tag" tab, and I realized that the tags cannot be sorted by alphabetical order when I clicked on the "name" tab next to the "popular" tab. For example, I'm writing "Server" in the tag search box, it brings the results in tag count order, then I click on "name" tab, and the search results are gone. Then I type "Server" again, but the results are in popularity order although "name" tab is active.
I wondered if the same thing happens on Stack Overflow and Server Fault, and the result was the same after several trials.
I tried these on both IE8 and Firefox 3.6.6.