When i ''mousseover'' a spell into the action bar i didnt see the spell detail

I would like do know why when I select a spell into spellbock i see the spell detail but when this spell is into action bar i just see the spell name and the rank...
Its a bug ? or normal condition... as far as I can remember, i have always see the spell detail when i mousseover it on retail...
you can write me on [email protected] if never you have already solve this issue

Thanks

Escape Menu -> Interface -> Help -> Enable "Enhanced Tooltips"