Part of the problem seems to be the misconception that pets can't break mez. There is only one instance where your pet won't break mez: if the mob is already mezzed and you tell your pet to attack it.
If the mob hits your pet and an enc mezzes it, your pet will break it.
If you send your pet on the mob and an enc mezzes it, your pet will continue attacking it (even if the pet itself isn't getting hit).
If a mob attacks you (with melee or an ae), your pet will attack it regardless of mez. This is probably the worst offender because often times a pet user will have their pet on a mob, then get ae'd by another mob. Their pet will not immediately switch targets, but as soon as its current target dies it's going to break mez on the add.
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