Star Trek IV: The Voyage Home (1986)

Suggested correction: According to the captain's log at the beginning, they have been on Vulcan for 3 months. As they prepare to depart, we see several Vulcan technicians moving equipment in and around the ship. It's quite conceivable that the bridge was reconfigured according to the crew's specifications to facilitate their use of the ship. This may seem a bit excessive, as the remodel includes the door onto the bridge, and the frame of the door, and possibly most of the rest of the ship. But it's not outside the realm of possibility. The real mistake, though, is why they would go to the effort of installing new workstations on the Klingon bridge and marking them with Klingon labels, instead of standard Federation text. Interestingly, though, the "Starfleet" style bridge layout of the Klingon ship is being used by the Klingons on the Bird of Prey in Star Trek V.

Vader47000

Answer: They only give him a schematic of the molecule. The man even says, "It would take years to decipher the matrix", or something like that.

Chosen answer: Scotty says "Why? How do you know he didn't invent the thing!" If the man was in fact the inventor, this would only cause a slight causality loop problem - he "invents" it because they gave it to him, but they only know it because he "invented" it. However, since Sulu said earlier in the movie that it was about 150 years too early for transparent aluminum, it would seem they do know this, so it wasn't a smart thing to do. Of course, the real flaw in the plot is that they need the tank to be transparent at all.

Myridon

Answer: The crew is resigned to the fact that their mission forces them to alter history in some fashion or another. McCoy just wants to acknowledge the gravity of their actions before they go ahead and do it, and Scotty's response is a cheeky way of reassuring him, "Hey, maybe it won't be that bad."

TonyPH