aye it hapened to me the other day fighting a named orc with fellows in zek. Our tank a guardian level 40 2 levels more than me couldn't get the aggro. After my pet disapeared the full grup of moobs jumped on me in few seconds I was tasting the ground.
I guess was my fault usually I wait until tank has the aggro then I give him support with pet, probably that day I sent the pet to early.