Other mistake: On board the USS Reliant as it orbits Ceti Alpha 6 the systems panels show ship diagnostic diagrams including a wire model of a Constitution class hull, something the Reliant doesn't have. (00:13:01)
Other mistake: When Captain Terrell shoots himself with the phaser, the phaser disintegrates along with his body, when it should have just dropped to the ground (as often shown in the various Trek TV shows). It wouldn't make sense to explain that the phaser disintegrated because Terrell was touching it, because then it would be impossible to explain why nothing happens to the ground that people are standing on when they get shot (Director's Cut). (01:11:20)
Other mistake: As the turbo lift doors open for Joachim to say his line, the diagram of the lift system on the back wall is of the Enterprise's system.
Other mistake: On the Reliant, as the woman turns and goes to activate the transporter, the blue diagram on the monitor above and to the right of her head is the port and top diagnostic views of the Enterprise, rather than the Reliant.
Other mistake: After Khan activates Genesis, David says the device will explode in 4 minutes. However, on the device itself we see the countdown begin at 999 at a rate of 2 per second. This correlates to about 8 minutes, 20 seconds.
Other mistake: After the Enterprise blows the port nacelle off the Reliant, the destroyed Reliant bridge is shown. The three sheaves of wires hanging from the ceiling should be on a tilt with the angle of the ship rather than straight down. Even accounting for the artificial gravity unit, which could have been damaged.
Chosen answer: According to the novelisation of the film the Genesis project was initially designed to be capable of creating an entire solar system. While the focus of the project eventually narrowed down to altering an individual planet, the sub-routines necessary to create a star were still in place and were activated when the device detonated within the nebula.
Tailkinker ★