I just got my unicorn to adult and she got Life Giver +2% damage to life magic.
With her equipped it shows my total bonus to life magic damage as +2%. It shows my other gear as +3 and +4 without the percentage mark on the character screen and the total of +3 +4 and +2% as +2%.
Is this a bug? Did I just take all the time to train her to adult for no benefit from this power?
I think you may have answered your own question, in a weird way. The 3 and 4 with no percentage symbol from your gear, are just "point" boosts - they are not a percentage. And they are not being calculated in the percentage total that displays in your stats. It just adds 7 points of damage to any damage spell you cast - no matter if you cast an imp or a centaur
The 2% on the unicorn gives you 2% boost to the base amount of the spell you cast. ( 100 damage becomes 102 and 500 damage becomes 510, assuming no other buffs/boosts)
Have you tried this - if you remove your unicorn, what is the damage boost percentage in your stats? and if you remove your gear, and equip just the unicorn, what is the percentage in your stats? this could be a quick way to see how the percentages are being displayed.
I had the same thing basically happen with my death wizard, but after posting about it, and logging into the game again, it was fixed. Try logging in and out again and see what happens.