How is the fluent conversation with spacecraft possible in Capricorn One?

In Capricorn One, the NASA mission control center maintains fluent communication with the spacecraft crew, which is obvious especially in the scene where the astronauts talk with their wives, even though the spacecraft was so far this would be impossible.

I would consider this just another logical glitch in the movie (which is full of them, IMHO), but the fact the signal from the spacecraft takes 21 minutes to reach Earth is repeatedly stressed in the movie just prior to these scenes. So I wonder, did I miss something? Is there any explanation, or is it really just an (obvious) error?