Board Thread:The Reference Desk/@comment-7657843-20170115121752/@comment-1789834-20170115202714

Before they release a DVD or video, they sometimes digitally enhance it by adding CGI. Some examples are the second version of The Five Doctors, which changed Tom Baker and Lalla Ward's scenes altogether, and which changed the Time Scoop from 2D to 3D. Other cases are updating The Ark in The Ark in Space to look more realistic, rather than a plastic model and updating gunfire to make it look less like 80s special effects.

In your case with this Movellan, it seems it was used to fix a plot hole of a gun not being fired yet something blew up. In the re-release, they added a firing of the gun to cause the explosion.

P.S. - this could also be a fan edit.