A question about FAST MEMORY

[mckimiaklopa]

As we all know,fast memory provides huge speed to many games since it skips many checks but it unfortunately causes many games to crash(crisis core,final fantasy type-0)

Question is
1:On crisis core and final fantasy type-0,why does the crash happen only when both frameskip and fast memory are on?Apparently,these games don't crash with frameskip off even though fast memory is on(tested this with multithreading on).

2.Why does multithreading affect the probability of crashes caused by fast memory?
On final fantasy type-0,turning off multithreading will not persist a crash even though BOTH FRAMESKIP AND FAST MEMORY ARE ON.