I evaluated the
functions, and supposedly it should something like \ast when executing
C-u *, but it doesn't happen.
I reread your initial email.. so look like you see nothing getting inserted when in do "C-u *"? That is odd.
Can you do the following and see if things work as intended? If they do, then there's something conflicting with your config:
1. Launch emacs -Q
4. M-x org-mode
5. Hit "C-u *"
6. You should see an asterisk being displayed, which is actually a prettified version of "\ast{}" which is what actually got inserted.
Also, please report your emacs and org-mode versions. I am using the latest build of emacs-25 branch from git and the latest build of org-mode master branch git.