How to beast craft? "craft" button stays gray/disabled for my Saqawine Vulture

Is beast crafting bugged? Do I have to do some quest to unlock beast crafting? My highest level char is 90 and I am running maps, but everything I try in the Blood Alter never unlocks/enables the "CRAFT" button.

I have a "Saqawine Vulture" and I am trying to Beast Craft with it. I go to the blood altar and put the "boss" beast in the first slot (upper left). Then I try filling in 3 more beasts but the "CRAFT" button stays gray no matter what combination of other beasts I try.

I have tried picking 3 other beasts which have the Rhoa icon (same species? like the Saqawine Vulture's icon). I have tried putting some armor on the "bench" area - maybe the target for the enchantment?

I don't understand what I am doing wrong? Is there a guide that shows what kinds of beasts to put into the slots or something? Did I miss a quest back in Act 2 to make Einhar enable my "CRAFT" button?

OK, I played with it more and if I click on the Title/Text of the recipe then the game auto-fills the slots with random creatures. If I try to fill the creatures in by hand/manually then it doesn't seem to ever enable the CRAFT button.

Is this a bug?