Op # n is the current Op,
Op # n + 1 is the next Op in the sequence.
If Op#1 moves to an inner pocket in a piece of metal that is 1" thick, and the pocket is 1/2" deep, then if you set the Safe/Clear heights for that, you have to ensure you can clear the 1" material. If the next job is in a separate/isolated area, that is at the same level as the inner pocket, but it has nothing surrounding it, you might be tempted to set the Safe/Clearance height for that 2nd Op based on it's local context, so, with Safe/Clearance adequate for 1/2" obstacles, but as you begin Op2, you are leaving Op1, and you have to pass a 1" obstacle.
I'm not sure that's what happened to you, just saying it could happen to someone and be confusing--but, it's never happened to me