IMDb presents information on titles as they originally were exhibited. As shown on episode one, www.imdb.com/title/tt0426236/combined, the runtime of the episode is 88 minutes. This represents the length of two standard episodes. On original airing the two episodes were combined with one set of end credits, so IMDb treats it as one episode. Even though it was later divided for syndication (these are the versions that appear on the DVD) IMDb will still number it as episode 1 which is naturally followed by episode 2, not 3, regardless of how the production company or network numbers the episodes.