Unable to add Rainbow Phoenix to HoM

Finally got the Rainbow Phoenix to level 20 and went to add it to the HoM, but it was not an available option. I can only cycle displays :S

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bah ... never mind ...
http://wiki.guildwars.com/wiki/Phoenix_%28pet%29

Yep, it's illogical but Rainbow Phoenix is a common pet while Imperial Phoenix is a rare pet.

Why is it illogical? The Rainbow Phoenix is a reward in itself, why would you get another reward for having it? O.o

It is illogical that Rainbow Phoenix is the most rare pet in game and it's ranked as common.

You get the Rainbow Phoenix after you either max ten titles or after you max 5 and fill out the entire HoM. What good would it do you after the fact?

Seconded. Some things are the end of a chain, not a new link to another chain. Otherwise the cycle would be unending.

I'm rather more confused why no other "finished campaign" pets have been added to the game.