Character mistake: When Uncle Ned calls Alcoholics Anonymous, he only dials 6 digits on the phone (instead of 7), but still the call successfully goes through.
Continuity mistake: When Alex tells Jennifer to play her clarinet outside Jennifer complains that its dark out, but you can see through the window that it is bright out. When they show it again it is dark.
Answer: A scene very similar to the one described happened on the show Mr. Belvedere that was on in the same time frame as when Family Ties was on. Perhaps this is what you are remembering.
af4dable ★