extglob pattern: @(/root) vs. @(root)

[Clark J. Wang]

See following:

# shopt extglob
extglob         on
# echo $BASH_VERSION
4.2.20(1)-release
# ls -d /root
/root
# pwd
/
# echo @(root)
root
# echo @(/root)
@(/root)  <-- ???
# echo @(/root*)
@(/root*)  <-- ???
#

I'm confused why @(/root) and @(/root*) do not work here.

-- 
-Clark