Filed a bug report on this, but for anyone looking to avoid it, the cause of the SLAs being cast at Caster Level 1 instead of the proper caster level is the Magister enhancement Master of Necromancy. It seems the SLAs are set to only scale to CL25 or something and so when you try to cast them at CL28 it casts them as CL1 instead. So for the time being just spec out your Magister's without Master of Necromancy.