Survival of the Fittest

[doofus]

I use the function IsUsableSpell() and GetSpellCooldown() to examine whether/when "Survival of the Fittest" becomes available.

This spell is only available if there is a Tenacity pet out.

If I am freshy logged in and there is no pet, or if I am freshly logged in with a non-tenacity pet, both the above functions return the true state of the spell, ie not available.

Once I summon a tenacity pet however, both the above functions behave as if the spell is available, regardless if the pet has been dismissed, or the pet is now a non-tenacity one.

The WoW client however correctly highlights the spell, so it knows. How does it do it ?