Casualty triggered abilities are confusing when trying to respond.
Steps:
AP casts Haughty Djinn. NAP casts Make Disappear, targetting Haughty Djinn, paying its Casualty cost. AP has Make Disappear in hand and Delver of Secrets on the battlefield. AP wants to use Make Disappear's Casualty ability to counter both copies of NAP's Make Disappear. However, because spells and abilities are presented in a confusing way, AP sees two "Make Disappear" on the stack, and thinks that is the right time to respond. However, the second is the ability that will create the copy. Casting at this point, especially when paying the Casualty cost, is a huge blowout.
If that explanation was confusing, then just imagine that that's how confusing it is to see in play.
Platform is Windows. Expected results are to be better able to discern a spell from its Casualty triggered ability. Actual results are being misled into casting a spell at the wrong time.