Invulnerable Mummies

[mrhills]

At level 12 I started soloing red con ghouls and yellow/white con mummies in nro right through until level 14 (as a necro). When I hit 14 I gated back to EC to sell all my stuff, and now that I've come back and started agro kiting undead again suddenly the mobs are invulnerable to my pets attacks when they weren't before. Are they supposed to be invulnerable to melee attacks or not? Is it down to what level my pet is when i summon it?