According to the description of Conjure Air Elemental spell, there are 60% chance that it summons 12HD Air Elemental, but actually it summons 8HD (HP 64) air elemental instead of it. Other Conjure Fire/Earth Elemental spells of the same spell level summon 12HD (HP 96) elementals correctly. So I think it's a bug.
And according to the description of Conjure Lesser Fire Elemental spell, it should summon 8HD fire elemental, but actucally it summons 12HD (HP 96) fire elemental. Other Conjure Lesser Earth/Air Elemental spells of the same spell level summon 8HD (HP 64) elementals correctly. So it's a bit overpowered.
I think two spells summon wrong creature files respectively.
I play BG2:EE 1.2 steam version and wish you would check it out.