tags slug problem

I noticed that tag slug doesn’t work in any themes including default.

slug like /tag/TAGNAME => show all posts NOT only that in tag

also in administration for

/wp-admin/edit.php?tag=work => shows all posts

also it doesn’t matter what permalink setting are, I tried all of them.

is it bug ?

you can see it on my site

http://maugustyniak.corpface.com

tags on the bottom widget

Thanks for any respond.