Pet Experience Penalty?

[Serendib]

Hello! I have looked for a definitive answer to this already on the forums but have been unable to find concrete proof one way or the other.

Is there currently an exp penalty for pets doing more than a certain % of damage to an enemy while you are soloing?

I have been told that for example, as a mage, if your pet does 51% of the damage to an enemy while solo, you will lose 50% exp for that kill while solo. But that this penalty will not apply if you are grouped. Is this correct? It seems to be true from my experience, but I have no numerical proof.