Other mistake: General Butarra holds his pistol to St. John's head asking him where the diamonds are, dry firing it when he doesn't tell him, so the chamber must be empty. He then proceeds to load a magazine into the gun, but never chambers a round, and then proceeds to shoot the radio when it receives a storm alert broadcast. (00:28:40 - 00:29:11)
Ground Zero - S4-E14
Other mistake: When Hawke blows up Yahara's plane, we see that the video feed in the holding cell where Locke, Santini, and Rivers are is actually from a 3rd person perspective and that it continues, but according to previous dialogue (and video up to that point) the camera was installed on the plane, so once Hawke blew the plane up, there should have been no more video feed. (00:40:35)
Continuity mistake: Just as Santini lands his helicopter after his rear rotor was destroyed, Hawke gets into his jeep and drives off. The number plate (licence) is reversed and Hawke's steering wheel is on the right side like British vehicles are. The next shot you see the shot has been flipped the correct way with both plate and steering wheel on the left side. (00:24:14)
Answer: I don't think it's ever explained why Mac refused to tell Hawke where St. John is.