Hi, I see the blunder in these way:
as the rulebook says "[...]whenever a wizard or a hero fails to issue an order as a result of rolling a 12."
0) roll the dice.
1)Apply modifiers --> is the order fail? --> the norm is that you fail with a 6+6 rolling.
2) Yes it is failed. --> has you rolled 12 (6+6 in the table)? --> Yes --> Oh no it is a blunder.
Well, I think this should count to all armies (ok, I never play lizardmen, so I read the divine guiance very quick and long time ago... so my opinion is very questionable here, but... if there is a 6+6 on the table... I think the lizard has blunder too

)