Plot hole: Major plot leak: How could Flint's ship get into the lake atop a tall volcano all in one piece? If he wanted to merely hide the treasure in order to recover it later, the whole setup, including the lake's draining system, would be totally unnecessary, and it looks all too deliberate for the ship to be sitting in the lake by accident (say, thrown in by a violent storm).
Other mistake: The sign which Silver reads says that one's got ten seconds to get away after pulling the chain. But in fact, after the monkey pulls the chain, fifteen seconds pass before the detonation (I've been counting).
Trivia: For those who wonder about the sign at the lake drainage mechanism: it is actually the original Japanese wording of the warning spelled in Latin alphabet.