Enchanter Pets Break Mez
 

I have noticed that Enchanter pets are breaking Mez when a mob which previously agro'd the pet is mesmerized. I can remember when this was patched on live. It was put in such a way that no pets could break mez. If a caster sent a pet after a mez'd mob, it would return the "that is not a valid target" message. This is a big issue which makes it pointless for enchanters to have a pet.

Enchanter pets (and all other pets) always broke mez. That was changed at a much much later date.

This didn't happen during classic afaik. Pets always broke mezzes, differentiating good and bad pet controllers, and even scarier for enchanters if they chose to use a pet. This was changed in a patch

June 5th, 2002

http://www.tski.co.jp/baldio/patch/20020605a.html