Its an interaction glitch between summons (Immortal acts as a summon for IK) and difficulty. If the troop-to-be-summoned is loaded into memory with difficulty boosted stats (due to either being on the initial team in the current battle or a previous battle), said troop gets the difficulty stat bonus applied on again using the base as whatever difficulty boosted stats the troop had. Warlord 4 gives x3 stats to the base, and x3 stats again to the summon, giving you a x9 troop.
I explained all the various interactions here:
No official word on a fix, to my knowledge.