When Elliot's daughters first see him as a ghost, their hair changes between shots.
When Joan goes upstairs to make a phone call, there are no skates on the stairs. In the next shot, Diane falls down the stairs after tripping over skates.
The song "Miss You Much," by Terry Lewis, is credited to Jerry Lewis in the end credits.
As a ghost, Elliot is only supposed to be visible in the dark. When he returns to his workplace as a ghost, other people can see him in the brightly-lit rooms. Elliot requires the light to be at a certain level or lower to be seen. People cannot see him at his workplace until his kids make it dark enough.
He goes through things as a ghost, but he doesn't sink through the ground or floor apart from somewhat inside his house.