Pets are burning.
 

Air and Fire pets are buffing no-stop. IE, fire is casting his DS and air invisibility all the time as soon as they are idle. Hiding the messages can be done thru filter :NP spells -> hide. But if you do so, you also hide every spell casted by every NPC, even the mobs you fight. Air does not loose invisibility when it start to melee.

Lucifer begins to radiate.
Lucifer begins to radiate.
Lucifer begins to radiate.
Lucifer begins to radiate.
Lucifer begins to radiate.
Lucifer begins to radiate.
Lucifer begins to radiate.
Lucifer begins to radiate.
Lucifer begins to radiate.
Lucifer begins to radiate.
Lucifer begins to radiate.
Lucifer begins to radiate.
Lucifer begins to radiate.
Lucifer begins to radiate.
Lucifer begins to radiate.
Lucifer begins to radiate.
Lucifer begins to radiate.
Lucifer begins to radiate.
Lucifer begins to radiate.
Lucifer begins to radiate.
Lucifer begins to radiate.
Lucifer begins to radiate.
Lucifer begins to radiate.
Lucifer begins to radiate.
Lucifer begins to radiate.
Lucifer begins to radiate.
Lucifer begins to radiate.
Lucifer begins to radiate.
Lucifer begins to radiate.
Lucifer begins to radiate.
Lucifer begins to radiate.
Lucifer begins to radiate.

I had that problem with Soulbinder Jera.(I made her a high level)
When I first changed from 6.2 to 6.3. Then one day I put a few npcs around her and her pet didnt flame anymore. I took them away and her pet never flamed again!!
I just checked in paw and seen a normal air type pet so maybe it fixed itself??? I have no Idea but Id just like to let you know you are not alone!!

For the original poster: Is the pet in question summoned by you the player or by a magician mob?

Player pets, RangerDown. I haven't fighted much magicians with air/fire pets, and can't confirm you that they don't do it either.

Do you see a buff actually land on you once the pet has casted his DS? FNW will have to confirm whether this is still in the code or has been changed, but the spell system used to be hard-coded to believe it was a mortal sin for any NPC to cast a beneficial spell on a PC. If you don't see a buff actually landing on you, then the pet sees that you don't have it and casts it. It never lands, so the pet keeps casting it, wondering why it won't stick.

If, OTOH, you do see a buff on you, then there must be something else at issue.

They cast their DS on theirselves, not on me.
I got some mobs that attacked me with endure cold, but i think it has nothing to see with that trouble.
I confirm that NPCs have the same problem, at least on PEQ, akstaff in Najena was doing it yesterday again.