Bestial Shift Interpretation?

This popped up incidentally in another thread, but without the explanation:   Why does The Naturalist's Bestial Shift allow you to (essentially) play through the card twice?  

I was playing a game against Akashbuta.  Naturalist had out (among others) Natural Born Vigor, Natural Form's Power, and Cornered Beast, and had been gaining HP and feeding cards to other heroes, but I wanted him to start doing some damage.   I played Bestial Shift, which in Gazelle Form reads: "The Naturalist gains 3 HP.  You may use a power now."   

As I read the card, that would allow me -- in "play a card" phase -- to (a) gain 3 HP, then (b) use The Naturalist's inherent power to shift to Crocodile form.  Then, in my "use a power" phase, between Vigor and Form's Power, I could use the Crocodile form's power and Natural Form both to do damage.

Instead what happened was this:

(1) I played Bestial Shift.

(2) Naturalist gained 3 HP.

(3) The game let me use a power, so I shifted to Crocodile Form (got it out of the trash).  

(4) Naturalist dealt 3 (+1) toxic damage, via the Crocodile text on Bestial Shift ("The Naturalist deals 3 toxic damage.  You may use a power now.")

(5) Still in "Play a card" phase, the game allowed me to use a power -- I used Crocodile Form's power to do 2 (+1) melee damage.  

(6) The game then shifted to "Use a power" phase.

(7) I used Natural Form's power to deal 1 + 1 toxic damage to two different targets.

(8) The game gave me the option to use Cornered Beast's power, but there were no targets under 3HP to destroy, so I just pressed "Skip," and ended Naturalist's turn.

What is the game mechanism that essentially repeats Bestial Shift's operation once you switch forms?   Not that I'm complaining by any means, but by my count, the game allowed me four power usages:  

(1) Naturalist's inherent power, upon playing Bestial Shift in Gazelle form;

(2) Crocodile form's power

(3) Natural Form's "Crocodile" power, and 

(4) Cornered Beast.

If you are in Gazelle a Form and play Bestial shift you get to activate the Gazelle part of the text. That gives you a 3HP and a power use.  Since you used that power to Transform into Crocodile and Bestial Shift is still resolving you get to activate the Crocodile text.  That gives you damage and a power use.   You chose the Crocodile power and then Bestial Shift finishes.  Since you have Natural Born Vigor, Natural Form's Power, and Cornered Beast out you have the ability to still use those powers.  So what you had happen is expected behavior.  

So the card hasn't finished resolving, even though I've already (a) gained 3 HP and (b) used a power (here, to change from Gazelle to Crocodile)?  

Yep.  By the time the first power use resolves you're now in Crocodile Form allowing that text to activate as well.